The Hardy boys were absolutely dumbfounded. The charge of theft seemed so absurd that they were at first tempted to laugh. But they saw that Chief Collig was in deadly earnest. His face was serious and his eyes regarded them sternly.

“The postal people have evidence against you lads,” he said. “A mail sack with about twenty thousand dollars’ worth of mail was stolen. They took out a warrant against you this morning.”

“Why, this is the craziest thing I ever heard of!” declared Frank hotly. “Us? Mixed up in that mail robbery? Why, we weren’t even near Bayport when it happened.”

“How do you know so much about when it happened?” asked the chief quickly.

“We were away down the bay all last night and we heard it over the telephone this morning.”

“Pretty good alibi,” said the chief. “And what time do you think the robbery occurred?”

“Last night.”

“Well, it didn’t happen last night. It happened yesterday afternoon, early. And you boys didn’t leave here in your motorboat until late in the afternoon. The robbery wasn’t discovered until last night. Where were you yesterday afternoon?”

“Why, we went in our roadster down to—” began Joe, but a warning kick from Frank silenced him. It would not do to tell Chief Collig that they had been in Beach Grove, seeking clues against Ducroy and his friends in the deserted cabin.

“Where did you go in your roadster?” asked Chief Collig.

“We went for a drive,” admitted Joe lamely.

“Where to?”

“Well,” said Joe, “we went down the Shore Road.”

“To the airport?”

“No.”

The chief pursed his lips. “You parked your car in Beach Grove,” he said. “I have a witness to prove it. And from there you walked through the bush to the airport.”

“We didn’t!” snapped Frank.

“Where did you go, then?”

“We just took a walk through the grove.”

“Can you prove it?” asked the chief.

“You’ll have to take our word for it, that’s all I can say.”

The chief shook his head. “I can’t take your word for it,” he returned. “The evidence against you is too strong.”

“Are you going to lock us up?” Frank asked.

“You’re under arrest. That’s my duty.”

“Won’t you let us go home first? We’d like to talk this over with our father.”

“He knows about it,” said Collig.

“But we want to see him, anyway. You come with us, Chief. We won’t try to run away.”

The chief considered this for a moment. “I guess there ain’t any harm in that,” he decided finally. He got up, put on his uniform cap, and led the way out of the office.

A department automobile was waiting at the curb and Chief Collig ordered the chauffeur to drive to the Hardy home on High Street.

“What makes you think we’re mixed up in this business?” Joe inquired. “Is it just because we were out on the Shore Road yesterday?”

The chief shook his head. “We didn’t know that until later,” he said. “After we began checking up on you two lads we found that you had been on the Shore Road.”

Frank was surprised.

“What made you check up on us? Why should you suspect us? We have never been in trouble before.”

“I know that,” returned Chief Collig. “You would never have been suspected hadn’t it been for the clues.”

“Clues?”

“There were clues found after the robbery. I think you’ll have a hard time explaining them.”

Beyond that, Chief Collig would volunteer no further information. The boys were puzzled and apprehensive. The chief’s mysterious reference to clues made their position seem more serious than they had at first imagined. Conscious though they were of their own innocence, they realized that their visit to Beach Grove made it almost impossible for them to prove an alibi and they readily saw that they might find themselves in a bad plight.

At the Hardy home they found Fenton Hardy awaiting them. Mrs. Hardy seemed anxious and frightened, particularly when she saw Chief Collig, but her husband managed to allay her fears.

“It’s all a bad mistake, Laura,” he assured her. “The boys have done nothing wrong. We’ll go into the matter thoroughly and see where the trouble lies.”

He ushered Chief Collig and his sons into the study, then closed the door.

“Well, Chief,” said the great detective easily, “this seems to be a bad mix-up. I didn’t meet the boys when they arrived this morning because I knew you wanted to have a talk with them and I didn’t wish to interfere. How do things stand now?”

“They’re under arrest,” returned Collig. “They wanted me to bring them home so they could see you, and I consented.”

“Under arrest, are they? Well, that’s bad. I thought they would be able to prove an alibi.”

“They can’t,” said the chief. “It isn’t my doing, Mr. Hardy. The post office people took out this warrant and if I didn’t arrest them, somebody else would.”

“I quite understand that, Chief.” Mr. Hardy turned to his sons. “Well, boys, this looks pretty bad. What have you to say?”

“It’s a big surprise to us, Dad,” said Frank. “The first we heard of the robbery was over the telephone this morning. We don’t know anything more about it than that. I think you know well enough that we’re innocent.”

Mr. Hardy nodded. “I’m quite sure of that. The fact is, however, that there is some damaging evidence against you. It will have to be explained. When were you at the airport last?”

“We’ve never been at the airport, Dad.”

“You’ve never been there at any time?”

“No,” said Frank. “We started out to visit the airport one day, but that was the time Giles Ducroy’s plane crashed when we were still some distance away. We turned back and returned to town.”

“Where were you yesterday afternoon?”

“We took the car and went for a drive out the Shore Road, to Beach Grove.”

“Did anyone see you? Can anyone prove it?” inquired Mr. Hardy, eagerly.

Frank shook his head. “No one saw us, so far as I know. You’ll just have to take our word for it.”

“That’s quite enough for me,” admitted Mr. Hardy. “But the police require something more substantial than that.”

“What’s all this about clues?” demanded Joe. “Chief Collig says they found some clues at the airport that seemed to connect us with the robbery. What were they?”

“We found a sweater, for one thing,” declared Chief Collig. “It was a blue sweater, with white trimmings.”

“I had a blue sweater with white trimmings,” said Frank promptly.

“Where is it now?” asked the chief.

“I lost it.”

Chief Collig nodded grimly. “You lost it at the airport. That’s where it was found.”

“My sweater? Found at the airport?” exclaimed Frank, dumbfounded.

“There are plenty of blue sweaters like Frank’s,” scoffed Joe. “How do you know it was his?”

“Because,” returned the chief, “his name was in it. It was on a tag inside the collar.”

Frank was silent for a moment. He realized how damaging the discovery of the sweater might be.

“I did have a tag with my name on it, stitched inside the collar of my sweater,” he admitted. “I guess it must be mine, all right. But I didn’t leave it there. I lost the sweater more than a week ago. I left it out in the barn one night and I haven’t seen it since.”

“Well,” said Chief Collig, “the sweater has been found. It was lying in the airport, in a place where you—where the thieves lay in hiding until the mail bags were left unguarded.”

“Anyone could have put the sweater there,” declared Mr. Hardy. “The person who took Frank’s sweater from the barn could have done that.”

“We have more evidence than that,” insisted the chief. He turned to Joe. “Let me see the soles of your shoes?”

Mystified, Joe elevated his feet. The chief looked at the soles, then referred to a paper which he removed from his pocket.

“You’ll find it hard to explain that,” he said, and placed the paper on Fenton Hardy’s desk.

Joe’s shoes had been bought at an exclusive sporting goods store in Bayport just a few days previously. They were new, and of an original design, the rubber soles were stamped in a peculiar manner. Probably no more than a few pairs had been sold since the shipment arrived.

The paper which Chief Collig produced had a penciled drawing which corresponded to the stamped design on the soles of Joe’s shoes.

“That drawing,” explained the chief, “was made from the footprints found at the scene of the robbery. What size of shoe do you wear?”

“Size six,” returned Joe.

“These footprints were made by a size six shoe. I went to the shoe dealers in town and I found that only one merchant handles shoes of that type. He says they are a new kind of shoe and that he has sold only one pair of sixes since they arrived. And he sold that pair to you. How do you explain that?”

“I didn’t leave the footprints there,” insisted Joe doggedly. “Someone else must have a pair of those shoes, same size as mine.”

“You are wearing the only pair of those shoes ever sold in Bayport,” declared Chief Collig. “The footprints were found at the airport in the mud. And there’s something else.” He took an object from his pocket and held it out in the palm of his hand. “Do you recognize that?”

“My knife!” exclaimed Frank.

“You admit it, eh?” The chief grunted with satisfaction. “You see the initials on it. J. H. to F. H.?”

“Joe gave it to me for Christmas, and he had the initials engraved on it.”

“I suppose,” sneered the chief, “you lost the knife at the same time you lost your sweater?”

“To tell the truth, I did.”

Fenton Hardy was pale and distressed.

“This looks very bad,” he said to his sons. “Have you any idea how the sweater and the knife came to be there, Frank?”

“None at all, Dad, unless the person who stole them from me left them at the airport.”

“And you, Joe? How about the footprints?”

“All I can say is that somebody else must have a pair of shoes like mine. Neither Frank nor I ever went near the airport.”

“I think,” said Fenton Hardy, “it wouldn’t be a bad idea if we went out to the airport now. We’ll have to look over the ground.”

Chief Collig accompanied Fenton Hardy and the two boys out to the airport, taking them there in his own car. The road entering the grounds was under guard, and the big hangars were closely watched, the authorities evidently taking no chances on a repetition of the robbery. However, Chief Collig was readily admitted and the party proceeded to a hangar where a newspaper photographer was busy taking pictures.

“I’d like to see those footprints, Chief, if you don’t mind,” said Mr. Hardy.

“They haven’t been touched,” said Chief Collig. “I gave strict orders they weren’t to be disturbed.”

Close by the hangar wall a few boards covered the ground. The chief raised them, and in the ground beneath they could see the clear imprint of a foot. The marks of the rubber sole were identical with those made by Joe’s shoes.

“Let’s see how your foot fits that,” suggested the chief, turning to Joe.

Without hesitation, Joe stepped forward. He placed his right foot in the print. It fitted exactly. When he removed his foot there had been not the slightest change in the original print in the ground.

“Yet you said you were never here before!” exclaimed the chief.

“I still say it,” Joe insisted.

“Then how do you account for that footprint? Same size, same marks, same everything.”

“Somebody must have had a shoe just like mine. That’s all I can say.”

The chief sniffed dubiously. Then Fenton Hardy, who had been examining the footprint, made a suggestion.

“Joe,” he said, “I want you to stand in the earth right beside that other footprint. Just walk across there, stand for a moment, and move away.”

Wondering, Joe obeyed. When he had done as his father asked, there were several new footprints in the soft earth. Mr. Hardy looked at them closely.

“What do you think of that, Chief?” he asked.

Chief Collig looked down at the footprints.

“Not much difference, so far as I can see,” he grunted.

“Not much. But there is a difference, isn’t there?”

“The footprints Joe just made don’t seem as heavy as the other one,” admitted the chief.

“They certainly aren’t. You can see how light the impressions are in the earth. That first footprint is pressed down quite heavily. You couldn’t help but see it, and I think it was meant to be seen. Joe’s natural footprints, on the other hand, are scarcely visible.”

“What of it?” demanded the chief.

“I mean,” said Fenton Hardy, “that the footprint you found here is not Joe’s natural footprint at all. It’s all very well to say that the size and the sole markings are identical, but there is more to a footprint than that. The first footprint was made by a very heavy person, as you can see by comparing it with the footprints Joe made just now.” He turned to his son. “How much do you weigh, Joe?”

“One hundred and twenty-five pounds,” Joe answered promptly.

“That’s not very heavy. But that first footprint was certainly made by a person weighing considerably more than that. The earth here is no harder now than it was at the time of the robbery, because it has been covered over by the boards, so I think the test proves itself. Then, to go further, wasn’t there another footprint, Chief? You have shown us only one, the conclusion being that the thief was a one-legged man.”

“There’s another footprint,” declared Collig. “Here it is.” He pointed to an impression in the earth a short distance away.

Fenton Hardy took a small folding measuring rule from his pocket and measured the distance between the two original prints. Then he measured Joe’s footprints.

“More proof,” he said finally. “The distance between these first two prints is a good seven inches more than the distance between Joe’s actual footprints. That proves that the man who wore those shoes was a good deal taller than Joe, with a longer stride. It also proves that when he made that heavy print in the mud he was not simply standing still, which might have caused the print to be heavier by reason of his weight. Otherwise his feet would have been close together. He was walking, just as Joe was walking a moment ago.”

Chief Collig was puzzled. Fenton Hardy’s deductions came as a rude shock, for the chief had already made up his mind that the Hardy boys were guilty and the evidence had seemed conclusive to him. He was not a man who admitted a mistake readily and he clung obstinately to his original belief.

“I don’t care how you figure it out,” he said roughly. “Your boys can’t explain how that sweater and the knife got here. And they can’t prove an alibi. I’m not going to let them go just because one footprint is a little bit heavier than the other.”

“You mean we’re still under arrest?” asked Frank anxiously.

The chief nodded. “You’re under arrest,” he said. “We’d better be starting back to the city.”

Fenton Hardy patted Frank’s shoulder.

“Never mind, Son,” he said. “I’m afraid I can’t convince Chief Collig just now, but at any rate I’m sure of your innocence. And we’ll prove it yet.”

There was nothing more the detective could do. They left the airport and got back into the chief’s car. Gloomily, they drove back to the city.

That afternoon, Frank and Joe Hardy were arraigned before a magistrate and, after the evidence had been presented, they were held for trial on the serious charge of robbing the air mail.

“Held for the robbery!” cried Joe, aghast.

“It’s the most ridiculous thing I ever heard of,” declared his brother. “What would we rob the mail for?”

“Gee, Frank, this will give us a black eye all right.”

“Don’t I know it? But I don’t think our real friends will believe a word of it.”

“Just wait till the newspapers come out. They won’t do a thing but spill it all over the front page!”

“That’s the worst of it. It will make mother feel pretty bad.”

“Yes, and when Aunt Gertrude hears of it she’ll say ‘I told you so.’ ”

“It’s a blamed shame, that’s what it is. I’d like to get back at the Chief for this.”

“So would I.”

This development caused a sensation in Bayport. When the afternoon papers came out with headlines, “Noted Detective’s Sons Held For Air Mail Theft,” friends of the boys and of Fenton Hardy could scarcely believe the news. On every hand people said, “There must be some mistake. The Hardy boys would never do a thing like that.” Scarcely anyone outside the police department could be found who actually believed the lads were guilty.

Nevertheless, this did not make the situation any easier for Frank and Joe Hardy. They were in jail, and the prospect of release seemed remote, because bail had been set in the heavy sum of fifty thousand dollars.

Fenton Hardy was not at all rich, and although he would have placed his entire fortune at the disposal of his sons, he was finding it difficult, if not impossible, to raise the big sum required for bail. He called on the boys late that afternoon and visited them in their cell, ruefully confessing that he had been unable to raise the money.

“I’m sorry, boys,” he said. “I hate to see you stay here in jail, particularly when I’m sure you’re innocent. But you won’t be here long. I’ll do my best to borrow the money to-morrow.”

“Don’t worry about us, Dad,” urged Frank. “Fifty thousand dollars is a lot of money.”

“Mighty slim evidence they’re holding us on,” complained Joe. “If they would only bring us to trial right away, we’d be acquitted sure.”

Just then they heard a disturbance in the corridor. Two men were arguing with one of the guards.

“But I tell you, we must see them right away!” demanded a familiar voice. “It’s an outrage! A scandal!”

“You’ve got to have a permit from the chief,” expostulated the guard.

“Permit! Bah! Here’s your permit! Now can we get past?”

“Hurd Applegate!” exclaimed Frank, in astonishment.

Two elderly men came hastening down the corridor toward the cell, a guard following close behind. One of them was indeed Hurd Applegate, the wealthy and eccentric man whose family treasure had been recovered by the Hardy boys, as related in the first volume of this series; “The Tower Treasure.” The other man was none other than Elroy Jefferson, the owner of Cabin Island.

“This,” declared Elroy Jefferson, standing in front of the cell and brandishing a newspaper, “is a shame! Nothing less than a shame!”

“A scandal!” fumed Hurd Applegate.

“A shame and a scandal!”

“You’re right, Elroy!” declared Mr. Applegate. “It is a shame and a scandal. I never heard of anything so disgraceful. The Hardy boys in jail! Impossible! And bail set at fifty thousand dollars! An outrage!”

“Idiotic!” raged Mr. Jefferson. He bowed to Mr. Hardy. “How do you do, Mr. Hardy. Mr. Applegate and I were just talking about our stamp collections when the boy came with the afternoon paper. We read it. We saw the headlines. ‘Hardy Boys in Jail.’ And at once I said: ‘This is an outrage!’ ”

“You did, Elroy,” affirmed Hurd Applegate. “And I said: ‘This is a scandal.’ ”

“Yes, Hurd, you said it was a scandal. And it is a scandal. So we put on our hats and came down here immediately.”

“It’s mighty good of you to visit us. You are—” began Frank, when Elroy Jefferson interrupted him impatiently.

“Good of us to visit you!” he stormed. “Do you think we came down here just to visit you? Do you think we’re going to let the Hardy boys stay in jail? Are we going to let them stay in jail, Hurd?”

“We are not!” said Mr. Applegate firmly.

Elroy Jefferson drew two slips of paper from his pocket.

“When we read in the paper that bail had been set in the outrageous amount of fifty thousand dollars, what did I do, Hurd?”

“You wrote a check,” said Mr. Applegate.

“I wrote a check. For twenty-five thousand dollars. And what did you do, Hurd?”

“I wrote one too. I insisted on it.”

“You insisted on it. You wouldn’t let me go bail for the boys myself. The sentiment does you credit, Hurd, but I would gladly have gone bail for the full amount.”

Frank and Joe sprang to their feet.

“We can’t let you do that!” exclaimed Frank. “That is awfully good of you——”

“Good of us!” snorted Mr. Jefferson. “Do you hear that, Hurd? They say it’s good of us. After what they’ve done for us!”

“It’s a pleasure,” declared Hurd Applegate.

“And now,” concluded Mr. Jefferson grandly, “if you will come with us we’ll go upstairs and turn over these checks as bail. The idea! The Hardy boys in jail! Most senseless thing I ever heard of! Why didn’t you call me up on the telephone? I would have been down here inside five minutes.”

“Me too,” chimed in Hurd Applegate. “I would have made it in three minutes, because I live closer.”

“Come along,” said Elroy Jefferson. “Let’s all get out of here.”

The two old gentlemen, fuming, led the way down the corridor, Elroy Jefferson waving the two checks that were to gain the Hardy boys their release.

Thanks to the generosity of Elroy Jefferson and Hurd Applegate, the Hardy boys were quickly released on bail. The two old stamp collectors scoffed when the lads sought to thank them.

“We’re not giving away fifty thousand dollars,” declared Hurd Applegate. “We know you won’t run away. And we know that when your case comes to trial you’ll be able to prove your innocence. So why should we let you stay in jail when you don’t deserve it?”

“Especially after what you did for us in the past,” said Mr. Jefferson. “We’re glad we can return the favor.”

That night, at home, the boys discussed the case with their father. Owing to the arrest of his sons, Fenton Hardy had been told by the authorities that his services in the airport mystery would no longer be required. This was a bitter blow, although he realized that the officials were justified in their action. But he resolved to continue the investigation on his own account.

“I’ll do all I can to clear you,” he promised. “And you must do all you can to clear yourselves. As it stands, they haven’t a very strong case against you, but it’s strong enough to be unpleasant. Our big chance lies in capturing the real robbers.”

“I’m sure that evidence was planted by Giles Ducroy,” declared Frank.

“Just wait until I get my hands on that skunk!” added Joe.

“I’m afraid you won’t lay your hands on him very easily,” said their father. “I wanted to have a few words with him myself, but he seems to have disappeared.”

“Disappeared!” exclaimed Frank, in surprise.

Mr. Hardy nodded assent. “He hasn’t been seen around Bayport for several days.”

“How about Newt Pipps and Ollie Jacobs?” asked Frank. “Are they still in town?”

Fenton Hardy seemed somewhat surprised at mention of these two names.

“Is that who Ducroy has been hanging around with?” he asked. “A bad gang! No, now that you mention it, Pipps and Jacobs have cleared out too. They haven’t been seen in Bayport for more than a week.”

“That looks bad,” said Joe. “If they weren’t up to something queer they wouldn’t have cleared out.”

“I’ll tell you where you may be able to find that pair,” said Mr. Hardy. “Do you know the Raven Roadhouse out on the Claymore Road?”

“I’ve heard of the place,” admitted Frank. “It’s supposed to be a mighty tough hangout, isn’t it?”

“Bad enough. Well, I’ve been checking up on Ollie Jacobs and Newt Pipps and I’ve learned that they make that place their headquarters. If you make inquiries there you may be able to find something about them.”

“We’ll make the inquiries, all right!” declared Frank. “I’m sure they know something about this business. What do you say, Joe? Let’s go out there right now and see what we can learn.”

“I’m with you.”

“Better be careful,” advised Fenton Hardy. “This roadhouse is a tough place and Jacobs and Pipps will likely have some friends there, so don’t give yourselves away.”

“We’ll watch our step,” promised Frank. “Don’t worry. We’ve got to clear up those mail robberies to clear ourselves, and I think the quickest way to go about it is to follow up the Ducroy gang. If they’re not mixed up in it from the start I’m a mighty bad guesser.”

The Hardy boys lost no time preparing for their journey out to the Raven Roadhouse, which was located some five miles from Bayport. Within half an hour they had said good-bye to their parents and had clambered into their roadster.

They drove down High Street, on through the business section of Bayport, and out to the highway. Frank was at the wheel.

“It was certainly mighty white of Mr. Jefferson and Mr. Applegate to go bail for us,” he said.

“They’re real friends,” Joe agreed. “The least we can do now is to clear up this business and show them that their confidence in us wasn’t misplaced.”

“We’ll do the best we can, although it doesn’t look very easy right now. That gang didn’t miss any bets in planting the evidence against us.”

“All the more reason why we should get them, and get them right. After what we heard in the cabin, I don’t think there’s much doubt that Ducroy and his crowd had something to do with the robberies.”

“Well,” said Frank, “we’ll go easy, and with any luck we ought to get some clues that we can follow up.”

They thought they would get to the roadhouse quickly, but a quarter of a mile on came to a detour sign. The road ahead was closed for repair.

“Just our luck,” grumbled Frank. “I know this road was open yesterday.”

“We’ve got to go around the old Rundle farm,” answered his younger brother. “That’s a dirt road, too, all the way.”

“Hope it isn’t muddy. It used to have some pretty bad mud holes in it when it rained.”

Fortunately for the Hardy boys, the detour road proved dry. The worst of the holes had been filled with cracked stone, so they got through without much difficulty.

In due time the Hardy boys approached the Raven Roadhouse. It was a long, rambling building, set back some distance from the road and approached by a winding driveway.

“I guess the best plan is simply to go in and ask about them,” said Frank.

He drove up to the front of the roadhouse. There were no guests present at this hour of the day. A fat man was lounging indolently against a veranda pillar.

The boys got out of the car.

“Too early,” grunted the fat man. “The fun doesn’t start here until after dark.”

“We’re not guests,” returned Frank. “We’re looking for somebody.”

A guarded expression crossed the fat man’s face.

“Who?” he asked abruptly.

Frank looked at Joe. “I don’t know whether we should tell him or not.”

Joe, taking his cue, looked dubious. “We weren’t supposed to tell. Still, it mightn’t do any harm.”

Frank looked around mysteriously. Then he lowered his voice:

“Have you seen Newt or Ollie around lately?”

The fat man regarded him shrewdly.

“Why do you want to know?”

“We have a message for him.”

“Who from?”

Frank shrugged. “Why should we tell you?”

The fat man was silent. Then he said:

“Is it from Sam?”

“Maybe. I’m not talking.”

The fat man seemed impressed.

“Well, you know how to keep your mouth shut anyway,” he said. “And that’s more than lots of people know. I guess you’re regular, all right. Well, I can put you in touch with Ollie Jacobs.”

“How about Newt?”

“He’s not here. I don’t know where he is right now.”

“Where is Ollie, then?”

“Down the road. You know where Greenfield village is, eh?”

Frank nodded. “About two miles farther down the road.”

“Well, that’s where you’ll find Ollie. He’s at the hotel. The clerk will find him for you.”

“Thanks. We’ll go on to Greenfield, then.”

“If you’d like to wait here,” suggested the fat man, “Ollie should be back in an hour or so.”

The Hardy boys had no desire to wait. They were on the trail of the elusive Ollie Jacobs and it did not suit their purpose to meet him face to face at the Raven Roadhouse. They thanked the fat man, got back into the car and drove away.

Within a few minutes they reached Greenfield. It was a meagre little village with a few unprosperous-looking stores and a ramshackle hotel.

“We’ll have to go easy here,” said Frank. “It won’t do to have Ollie Jacobs see us.”

“What should we do? Wait out in front of the hotel?”

“He would probably see us first. No, I think it would be better to go inside and take a look around. Once we locate him we can keep out of sight and then follow him later.”

They parked the roadster in front of the hotel and went inside. The Clerk, a seedy little man with shifty eyes, regarded them with suspicion. By way of explaining their presence, the Hardy boys bought some newspapers and a few chocolate bars, then sat down in the lounging chairs in the main office.

“We’ll just sit tight for a while,” whispered Frank. “If Ollie Jacobs is in the hotel, he’ll probably pass through here on his way out.”

The words were no sooner out of his mouth than Joe gave his brother a sharp nudge and hastily began to unfold one of the newspapers. Frank glanced up. Coming down the stairs was Ollie Jacobs.

The man did not see the boys, or at least did not recognize them, for Frank quickly lowered his head, then he, too, spread out a newspaper so that it concealed him from view. Thus, to the man descending the stairway, the two lads appeared intent on the papers, and their faces were completely hidden.

Another man was coming down the stairs a few steps behind Ollie Jacobs. When the pair reached the office, instead of going toward the door, they sauntered over and sat down a few feet from the Hardy boys.

Frank and Joe were trembling with excitement. Behind the newspapers they were safe from observation.

“I won’t go a cent over eight thousand, and that’s final,” they heard Ollie Jacobs saying.

“We’ll split the difference,” returned the other man, in a wheedling tone. “Make it nine thousand dollars cash.”

“Nothing doing! I’ll give you eight thousand dollars. Take it or leave it.”

“An airplane for eight thousand dollars!” exclaimed the other. “I can’t do it. I’d be losing money.”

Ollie Jacobs laughed. “Even at eight thousand, you’ll be making a good profit.”

“Eighty-five hundred,” pleaded the bargainer.

“I’ve made my offer and I won’t raise it a nickel. I’ll give you eight thousand dollars in cash the moment the airplane is turned over to us. You have the machine within five miles of here, you say. Well, I can have the money within half an hour and we’ll close the deal. So make up your mind, for I can’t be wasting time. If I can’t buy your airplane I can easily find another one.”

Ollie Jacobs got up from his chair. The other man rose quickly and seized him by the arm.

“All right. All right,” he said hastily. “It’s just downright robbery, but I’ll sell you the plane for eight thousand. I won’t be making a cent.”

“That’s your lookout,” returned Jacobs coolly. “You don’t have to sell it.”

“I’ll have the plane ready for you at my farm. As soon as you turn over the money, the machine is yours.”

“The money will be in your hands within half an hour. Are you going to the farm now?” said Jacobs.

“I’ll go there right away and get the plane in shape.”

“Be sure you have the tanks full of gas. I want everything to be in perfect running order. That’s the only condition of sale. I want the plane to be in readiness.”

“You can step right in it and start flying the minute you buy it,” insisted the other man. “And you’re getting a bargain, let me tell you. There isn’t a better machine on the market. If you bought that plane from the factory it would cost you fifteen or twenty thousand dollars.”

“A new plane would cost that much. Yours isn’t worth five. It’s an old crate, almost falling to pieces. You’ve been flying it for more than four years now. Well, the deal is made. You go to the farm and get the machine ready. I’ll be over to take possession in half an hour.”

The two men went out the door and descended the steps. Apparently Ollie Jacobs did not notice the roadster belonging to the Hardy boys, for, after halting for a moment on the sidewalk, he strode briskly down the street in a direction opposite to that taken by his companion.

Frank lowered his newspaper and looked at Joe.

“What do you make of that?” he demanded.

“Ollie Jacobs buying an airplane! That fellow never had eight thousand dollars of his own in all his life.”

“He seems to have it now,” said Frank. “There’s something in the wind.”

“I think we’d better follow him.”

They sprang to their feet.

“There’s no time to lose,” Frank agreed. “I’d like to know what Ollie Jacobs is planning to do with that plane!”

When the Hardy boys left the hotel they saw Ollie Jacobs about a block away, walking quickly down the street toward the outskirts of the village. As unobtrusively as possible, they followed him. They soon found that there was little need for caution, as Ollie Jacobs evidently had no suspicion that he was observed, and not once did he look back.

Leaving the sidewalk, their quarry struck out along a country road in the direction of an abandoned house. Here, instead of passing by, he vaulted the fence, crossed the unkempt yard, and disappeared into the building.

“We’ll have to go carefully,” said Frank. “I’ll bet he’s meeting the others there.”

“That’s where he intends to get the eight thousand dollars, I suppose.”

“Chances are, they’re watching. We’d better go around by the back way.”

At the end of the street, therefore, the Hardy boys did not follow the road, but instead made a detour through the fields, coming around at the rear of the old house. There they made their way carefully across the yard. They knew that they risked detection in so doing, but they were obliged to take this chance.

Luck was with them. They crossed the yard in safety, evidently unobserved by anyone in the house.

They crouched beneath a window and listened. From inside the house they could hear human voices. Frank raised himself slightly and peeped through the window. The room was empty. The voices seemed to be from the front of the house.

He gestured to Joe, and silently they crept on to the next window. Here they had better luck. The window was partly open and they could clearly hear the voices of the men in the room beyond.

The first voice they heard was that of Ollie Jacobs.

“Well,” he was saying, “I guess we can each chip in and make up that money. The plane is waiting for us.”

A familiar voice answered:

“Eight thousand dollars is a lot of dough. But it will be worth it in the long run.”

Frank and Joe exchanged glances. They recognized the voice. Giles Ducroy!

“Are you sure the plane is all right?” demanded the third man—Newt Pipps.

“It’s old, but it’s plenty good enough for our purpose,” returned Jacobs. “She’ll hold four or five men.”

“I don’t want to go flying in some old rattletrap that’ll bust all to pieces in mid-air and kill us all,” demurred Newt.

“Don’t worry. I’ll be in charge of the plane,” declared Ducroy. “I could fly a baby carriage if it had wings. Your precious neck is safe enough.”

“Well, here’s twenty-five hundred dollars,” said Jacobs. “That’s my share.”

“And here’s mine,” said Newt.

“And I’ll make up the other three thousand,” said Ducroy. “You never spent money any better. If this pans out all right it will bring us fifty thousand dollars at least.”

“You say it’s the twenty-eighth or twenty-ninth?” asked Ollie Jacobs.

“Yes,” answered Ducroy. “Pay day is on the first of the month, and they always send the money a day or two ahead.”

“It’ll be a big haul if we get away with it,” declared Newt Pipps. “But it’s certainly risky.”

“You’ve got to take chances to make big money,” Ducroy answered. “Fifty thousand dollars isn’t to be sneezed at.”

“I’m satisfied,” said Ollie Jacobs. “I think we can get away with it. Fifty thousand dollars looks mighty good to me. I think we ought to go right over to the farm, buy this plane, and start out.”

“Where do we go first?” asked Newt.

“There’s an airport about thirty miles from here,” Ducroy said. “It’s just a small flying field—the Riverside Field, they call it. We can take the plane there and wait until everything is ready.”

“What if we’re caught?” asked Newt. “The police in Bayport are on the lookout for us, you know that. If they find out where we are, it will ruin everything.”

“We have the plane, haven’t we? If they find out where we are, we’ll simply fly somewhere else, and dodge them. I have everything all figured out. We’ll be quite safe.”

“Then let’s get going,” said Ollie Jacobs impatiently. “We’re just wasting time by arguing here.”

There was a scuffling of feet, then the slam of a door. After a few moments the Hardy boys peeped around the side of the house and saw the three men going down the road in the direction of the village.

“It looks as if we’ve stumbled on something,” said Joe.

“I wonder what they’re going to do with that airplane. One thing is certain—there’s something in the wind for the twenty-eighth or twenty-ninth of this month.”

“What date is this?”

“The twenty-sixth.” Frank watched the receding figures of the men. “I suppose we ought to follow them.”

Joe demurred.

“Why should we? There’s no chance of losing them now. We know the name of the airport they’re bound for, and we can go there in the car and wait for them.”

“That’s right. We’ll go on to Riverside Field and keep an eye on them from there. But first of all, I think we ought to call up dad and let him know what we’ve learned.”

Joe agreed that this was a sound suggestion. The boys waited until the trio were out of sight, then hastened on toward the village. Their first concern was a telephone, and as they did not want to go to the hotel, in case some of Ollie Jacobs’ friends might be within earshot, they lost some time seeking the telephone exchange, which they finally located in the rear of the post office.

There they put through a call to their father in Bayport. After a wait of about ten minutes, the call was answered. The operator turned to them.

“Mr. Hardy is not at home. Will anyone else do?”

“Anyone at that number,” assented Frank.

He picked up the receiver and heard his mother’s voice.

“Hello, Mother. This is Frank calling.”

“Yes, Frank. Where are you?”

“We’re at a little village just outside the city. Where is Dad?”

“He left for New York an hour ago,” answered Mrs. Hardy. “He just received a telegram calling him to New York on special business.”

Frank was disappointed.

“That’s tough luck. We had some news for him. Well, we’ll just have to carry on alone. If we’re not home to-night, don’t worry about us. We’ve picked up some information that may clear up all this fix we’re in.”

“Don’t stay away too long, Frank,” said Mrs. Hardy. “The police were making inquiries a little while ago.”

“The police? Why?”

“They think you may have run away. They’re afraid you have jumped bail.”

This news came as a stunning shock to Frank.

“Why, that’s nonsense!” he exclaimed hotly. “We’ll be back as soon as we can, and if they make any more inquiries you can tell them so. And when we do come back, they won’t have any further excuse for holding us, for we’ll have the real mail robbers with us.”

“I hope you are right, Frank. If your father comes back, I’ll tell him you called.”

“All right, Mother. And don’t worry about us. We’ll be back home as soon as we can get away.”

Frank hung up the receiver and paid the cost of the call. When he turned toward Joe, however, he found his brother standing in the door, gazing up at the sky.

“They’re away already!” exclaimed Joe excitedly. “Look!”

Frank ran to the door. Joe was pointing up at the clouds. High above them soared an airplane, drumming its way toward the south.

“I saw it rise,” said Joe. “It took off from one of those farms back of the village. It’s Ducroy’s crowd, sure as guns.”

“On their way to the flying field already. Well, we’d better be moving.”

They hurried down the street toward the hotel, where they had left the roadster. On the way, Frank told Joe the result of his telephone call. Joe too was disappointed that they had not been able to get in touch with Fenton Hardy.

“It means we have to play a lone hand, that’s all. What do you think we should do next, Frank?”

“I think we ought to tell the authorities.”

“We’ll warn them to watch the airplane hangars on the twenty-eighth and twenty-ninth,” said Joe. “But we mustn’t lose sight of Ducroy and his cronies.”

They looked back. The airplane was merely a blur in the distance. The boys realized that they had no time to lose. They scrambled into the roadster. Frank threw in the clutch and the car shot forward. Within a few minutes they were speeding down a road toward the south in the direction of the Riverside Field.