“Are you joking, Frank?” asked Billy, though he should have known his comrade better than to believe Frank would try to play any silly trick for the sake of giving them a thrill.

Pudge opened his mouth, but for a wonder even one of his queer favorite expressions failed to drop from his lips. In fact, Pudge was rendered temporarily speechless by the astounding nature of Frank’s communication.

“Not at all, Billy,” said the other, trying to act as though he might be telling them something of small importance. “I watched while I was sheltered under the plane, and twice I saw it shake a little as though some one might be holding the door ajar so as to hear better.”

“Door!” echoed Billy helplessly, as though more puzzled than ever.

“The door of the empty locker we thought we might need for storing things away, but which has never been used,” Frank explained.

“Gee whillikins! now I understand what you mean, Frank,” said Billy. “There is plenty of room in that locker to hold a man curled up.”

“Popguns and pyramids, but how could he ever get there when we’ve been sitting around all morning?” asked Pudge, in a hoarse whisper.

“Only in one way,” Frank told him. “Before they left here last night they must have fixed him there in the locker, believing we’d be back again sooner or later, when some information of value might be picked up.”

“Oh! my stars, Frank,” Billy ejaculated huskily. “What if, after all, he’s heard enough talk here to guess about that big raid?”

Frank looked very serious.

“It’s true that we’ve been pretty careful,” he said, “and most of the time just whispered while we talked about it; but all the same a man with the ears of a spy might have picked up enough to arouse suspicions, and once that’s done the rest would come easy.”

“What can we do about it, Frank?” asked Billy.

“Our good friend, the Major, has extended the invitation to us so that in a way I feel we’re responsible for the secret being kept,” Frank went on to say, as though he might be revolving certain conditions in his mind before deciding.

On hearing him say that Billy began to work the muscles of his right arm, at the same time opening and closing his fingers, as though eager to clutch something.

“I agree with you, Frank,” he hastened to say. “The great secret has been placed in our keeping, and for one I would feel pretty small if it leaked out through any fault of ours. We’ve got to cage that spy as sure as you live.”

“Punkins and partridges, that’s right!” muttered Pudge, who, while not as a rule pugnaciously inclined, could nevertheless assume what he was pleased to call his “fighting face” when occasion arose.

“I’m glad to find both of you are of the same mind,” Frank said. “The only question is to decide what our plan of campaign shall be.”

“P’r’aps some of those Tommies in khaki would be only too glad of a chance to step in and collar the spy?” suggested Pudge.

“But there are three of us here,” objected Billy, “and I don’t see why we should want to call on the soldiers for such a little thing. After we’ve grabbed Mr. Spy and have got him tied up it will be time enough to figure on handing him over to the authorities.”

“That’s what’s worrying me,” admitted Frank.

“About handing him over, do you mean?” Billy demanded.

“Well, you know what the fate of a spy always is,” the other said. “We are supposed to be neutral in this war business. No matter whether our sympathy lies with Belgium, Germany, or France, we’ve got to try and treat them as much alike as we can. Our company has been negotiating with the French Government for a long time, now, over this contract, and so, of course, we have to favor them if anybody; but boys, not one of us would like to feel that we were the cause of a spy being shot or hanged.”

“Oh well, we could kick him off the place after we got him out, Frank,” suggested Pudge so aggressively that Billy chuckled, and started to smooth the fat chum down the back, just as one might a pugnacious rooster who was boiling with a desire to plunge into carnage.

“That sounds all right,” Frank told him; “but you forget the one important thing. He has some knowledge of this raid, and if we let him go it may mean a great disaster to the fleet of seaplanes taking part in the dash up the coast.”

“Whew! looks like we might be what my father would say was between the upper and the nether millstones,” remarked Billy.

“Gatling guns and grasshoppers,” Pudge added, “my father would go further than that, I guess, and say we were between the devil and the deep sea. But Frank, you’re the one to decide that question. What shall we do?”

“There is a way,” Frank announced, “by which we could settle it so the man wouldn’t fall into the hands of the military authorities, who would execute him, and at the same time he could be kept from betraying what he may have learned.”

“Glad to hear it,” said Pudge; “because I don’t want to know I’ve been instrumental in standing a poor fellow up before a file, and getting him filled with cold lead. Tell us about it, please, Frank.”

“After we’ve captured the man we’ll get word to the civil authorities, saying we’ve caught a thief in our hangar, and asking them to keep him safe for two or three days. I’ll go and see the Major myself, and get him to promise that the man will be treated only as a thief and not as a spy.”

“You’ve guessed the answer, Frank,” announced Pudge, with the enthusiasm he always showed when the leader of the aviator boys blazed a trail out of some wilderness in which they had lost themselves.

“Then the sooner we get busy the better,” hinted Billy, again working that good right arm of his as though it might be rapidly getting beyond his restraint.

“We have no firearms, though,” suggested Pudge.

“There’s no need of any,” Frank told him. “I’ll hold this wrench in a way that’ll make it seem like a six-shooter. The rest of you can help pile on the man when we drag him out of the locker, either feet or head first, it doesn’t matter which.”

“Just give me a chance to sit on him, that’s all!” threatened Pudge, at which Billy could be heard to chuckle, as though he pitied anyone who went through that far from enviable experience; perhaps Billy knew from his own associations with Pudge what such an operation meant.

“Now, here’s the way we’ll fix it,” began Frank. “I’ll step over again to the other side of the hangar to work at the motors of the Sea Eagle. Pretty soon you’ll hear me calling to you both to come around and see what a clever little arrangement I’ve fixed up.”

“Which will, in other words, mean the fun is about to begin?” commented Billy.

“When you join me,” continued Frank, “we’ll jabber for a minute, during which I’ll say we might as well go to town and get something decent to eat at noon. That will be apt to put him off his guard. Then we’ll all tiptoe over to the locker, and at a signal throw the door open. As soon as you glimpse him, take hold, and start to pulling like a house afire. That will keep him from trying to fight back or use his weapon, for I guess he’ll have a gun of some kind. Understand it all, boys?”

“Go on, Frank. Please don’t wait any longer than you have to,” pleaded Billy.

So Frank, a minute or two later, called to them to come and see what a splendid little change he had made in the gear of the deflecting rudder of the big seaplane.

It was a thrilling moment for the three boys when they began to move in the direction of the locker where Frank believed a spy had taken refuge many hours previously. As he had suggested, they walked on their tiptoes, each fastening his eager gaze upon the door which they expected to presently pull suddenly open.

When they had taken up their positions according to Frank’s plan, he gave the expected signal.

“Now, everybody!”

The locker door was dragged open in spite of the fact that something seemed to be clinging desperately to it from the inside. No sooner had this been accomplished than the boys, stooping, seized hold of the doubled-up figure they could see in the cavity under the bench, and started to drag with might and main.

Although the man in hiding made a powerful effort to resist the pressure brought to bear upon him, he was hardly in a position to do much.

They dragged him out, squirming like a rat taken by the tail, and trying to hold on to every object, however small, as a drowning man will catch at a straw. No sooner was he in full view than Pudge dropped down on his back with all his force.

A dismal groan announced that the breath had been pretty well driven from the spy’s lungs; and before he could recover his wits enough to try and produce any weapon Frank clapped the end of his wrench against his temple while he called out in very commanding tones:

“Don’t try to draw a gun or you are a dead man! I’ve got you covered, and will pull the trigger if you so much as move a hand!”

Having in this manner caused the prisoner to behave, Frank hastily searched his pockets and confiscated a stubby little revolver which he found there. Then he told Billy to tie the man’s wrists together, placing them behind his back, with a stout piece of tarred rope that lay within convenient reaching distance.

“Now he’s helpless, and we can let him get to his feet if we want,” said Billy; but Frank thought otherwise.

“It’s better to be on the safe side,” he observed. “So use the balance of the rope around his ankles, Billy. I want to leave you two here while I go to town and make arrangements through Major Nixon to have the man held simply as a thief and not as a spy. I’d like to know he couldn’t get away.”

They found that he was rather a small man, with a cunning face. He did not look very much like a German, and possibly had been picked out for his hazardous pursuit on that very account.

To their surprise he addressed them in the best of English.

“I am an American citizen, you must know, and I have the papers to prove it. My name is Hans Larsen and I came from Sweden many years ago.”

“Oh! is that so?” remarked Frank, who had lately read that many Germans across the sea had been able to secure the naturalization papers belonging to others in order to cross to Sweden or Italy without being taken prisoner by the English naval men, and Frank rightly guessed the spy had fortified himself in that way so as to have some means for escaping death in case of capture.

“Then what were you doing hidden in that locker?” demanded Billy.

“I have no money, and I was hungry,” said the man. “I came here to pick up something I could sell for a few sous, and get some bread. Then I heard voices and afraid to be seen I crawled under there. Let me go and I shall never bother you again.”

Billy laughed in his face.

“They say a lame excuse is better than none,” he remarked, “but when Frank pulled that fierce-looking gun out of your pocket I saw a bright coin fall to the floor. Here it is, and a gold coin in the bargain. An English sovereign at that. I wonder why anyone should go hungry long in Dunkirk these days with all that money in his pocket? Don’t try to trick us, my man. We know why you were hidden in that locker, and you don’t need to be told what a spy can expect when caught in the act.”

The man shut his teeth hard together, and gave a little groan, but said nothing. He evidently expected that the fate he may have dared so often had at last found him out.