“What will you do with the spy, Lord Hastings?” asked Frank.

“Shoot him,” was the brief reply.

Frank was silent for some moments.

“It’s terrible to think of it,” he said at last. “Still, I suppose it must be done.”

“It must,” returned Lord Hastings.

“Will there be need of a trial first, sir?”

“A trial, of course, is only a formality. Nevertheless, he must have one.”

“When, sir?”

“The court martial will sit in half an hour.”

“And will be composed of how many, sir?”

“Six. Mr. Templeton, yourself, Johnson, Smith, one of the sailors and myself. It will sit here in my cabin.”

“Very good, sir. I shall be here.”

Half an hour later the prisoner faced his judges. Lord Hastings addressed him.

“Prisoner,” he said, “what have you to say in extenuation of your actions?”

“Nothing,” was the brief response.

“Have you anything to plead why sentence of death should not be pronounced on you?” continued Lord Hastings.

“I have nothing whatever to say,” was the firm response.

The six judges consulted together for some moments. Then Lord Hastings turned again to the prisoner.

“As president of this court martial,” he said slowly, “I sentence you to be shot at six o’clock.”

He drew a watch from his pocket and glanced at it.

“It is now five,” he said. “You have one hour in which to prepare yourself to meet your maker.”

The prisoner bowed his head in assent. Then, at a signal, he arose and was conducted from the room.

Six o’clock came all too swiftly for Frank and Jack, who could but look with horror upon this cold blooded way of disposing of a man, simply because he was a spy.

The D-16, feeling her way carefully, had come to the surface, and now the prisoner was conducted to the bridge. He took his stand at one end and waving aside a proffered bandage, faced his executioners unflinchingly.

A firing squad of six men took their positions opposite him. Much to his chagrin, Jack had been put in command of the squad, and it was his duty to give the word that would snuff out the life of a fellow being.

But Jack was not the lad to refuse to obey orders, and now he stood behind the squad.

“Ready,” he said calmly.

“Take aim!”

But before he could give the word to fire, the prisoner, who up to this moment had been standing with folded arms, suddenly flung himself into the sea.

“Fire!” cried Jack, and the sailors poured a volley after him. Then all rushed to the rail and watched for him to reappear.

A few minutes later a head appeared a short distance away. It became at once apparent that the spy had not been touched.

Immediately Jack rushed to the side of the vessel and also flung himself into the sea. The erstwhile prisoner saw his action and struck out vigorously toward the south, where, in the gathering darkness, he could make out dimly a strip of land.

But Jack was a powerful swimmer and gained rapidly on the spy.

Perceiving that he could not out-swim his pursuer, the spy slackened his stroke, and just as Jack came up to him, dived. As he went down, he caught Jack by the legs and pulled him under also.

Taken at a disadvantage Jack struggled in vain to free himself. He was at a further disadvantage also, for the spy, before going under, had caught a long breath; whereas Jack had gone under sputtering and gasping.

But help came to Jack from a source he did not expect. When he had jumped into the sea in pursuit of the spy, Frank had done likewise, for he divined that Jack might have trouble recapturing the prisoner. While he was not such a powerful swimmer as Jack, he was nevertheless close at hand when the spy pulled his chum under.

Frank acted without an instant’s hesitation. Drawing his revolver and grasping it by the barrel, he also dived. Down and down he went, and then close beside him he became aware of the struggling figures.

The water was very dark, but the lad could dimly distinguish the form of his friend from that of the spy. Going close, he raised his revolver and brought it down on the spy’s head with all his force. At the same time he stretched forth his other hand, and seized the spy by the shoulder.

Freed of the hold on his legs, Jack immediately shot to the surface, where he filled his lungs with fresh invigorating air. A moment later Frank, still grasping the spy by the shoulder, appeared by his side.

“Lend a hand,” he called, “and we’ll get him back aboard.”

Jack, now greatly refreshed, did as his chum ordered and the two lads, supporting the body of the spy between them, swam back to the submarine, where willing hands helped them over the side.

Lord Hastings immediately took charge of the spy.

“Stretch him out there till he recovers consciousness, and then proceed with the execution,” he ordered.

The body of the spy was stretched out on the deck, and two sailors bent over him. Then one started back, and took off his cap.

“The execution will not take place,” he said.

“What do you mean?” said Lord Hastings. “Is he——”

“Yes,” interrupted the sailor, “he is dead.”

“By George!” muttered Frank, “that blow over the head.”

“No,” said the sailor, “it is the water that did for him.”

“I’m glad of that,” said Frank simply.

“Prepare the body for burial immediately,” ordered Lord Hastings. “We’ll remain on the surface until after he has been buried, then we’ll submerge and continue our course.”

The work of preparing the spy’s body for burial was only a question of minutes, and when it had been turned over to the mercies of the sea, Lord Hastings gave the command:

“Submerge immediately, Mr. Templeton.”

All descended from the bridge, the little vessel was made snug and comfortable, and disappeared from the surface of the sea.

“Shape your course due east, Mr. Templeton, and steam at 7 knots,” ordered Lord Hastings. “Mr. Chadwick, you will take your post and watch for mines.”

“Very good, sir,” replied both lads, and departed on their respective duties.

In the darkened room in the bow of the vessel, with the powerful searchlight lighting up the murky water ahead, Frank kept careful vigil. Hour after hour he sat there in silence, hardly moving from his first position.

The D-16 forged ahead but slowly, for there was no need of undue haste and Lord Hastings was not minded to take unnecessary chances.

Frank glanced at his watch.

“Midnight,” he muttered to himself. “Only one more hour and then I can turn in for the night.”

Still the minutes passed without incident. Finally, at a few minutes to one, Frank, after a second glance at his watch, arose and stretched himself.

“Guess nothing will turn up in my watch,” he told himself.

But the lad was mistaken.

For one moment he had taken his eyes from the water ahead, and now, glancing forth once more, he beheld a sight that moved him to instant action. His eyes fell upon a large object directly ahead, a scant hundred yards.

Quickly the lad jumped to the bell that signalled the engine room. And almost as quickly the speed of the vessel was checked. But the nose of the submarine was now but inches from the dark looking object ahead.

Lord Hastings’ face appeared in the room.

“What’s the matter?” he demanded.

“Looks like a mine, sir,” replied Frank quietly.

Lord Hastings advanced until he could get a good look at the object. He peered at it long and carefully, then turned to the lad.

“You are right,” he said. “It is a mine. Had you perceived it an instant later we undoubtedly would be in the land of the missing by this time.”

Frank flushed at this, for he realized perfectly that had he been paying strict attention to his duties, the submarine would not have come this close to danger of destruction. But he said nothing.

The mine extended well up toward the surface of the water, but the bottom of it was in plain sight.

“I suppose the best thing to do is to dive under it,” said Lord Hastings.

“My idea, too, sir,” agreed Frank.

Lord Hastings turned on his heel and left the compartment, and a moment later the vessel began to sink lower and lower into the sea. Frank still stood on watch, and when he was certain that the D-16 would pass beneath the mine without danger of striking it, he gave the signal and the vessel headed forward once more.

Lord Hastings entered the compartment again.

“The chances are there are more of them,” he said, “so we shall have to be very careful. I’ll have Mr. Templeton take the next watch, for we cannot keep too sharp a lookout.”

Frank nodded his head in assent. Lord Hastings left.

Five minutes later Jack appeared at Frank’s side and the latter turned to go. Suddenly he whirled about and spoke to his chum.

“You must be more careful than I was,” he said quietly. “I was almost the means of sending us all to the bottom for good.”

“What do you mean?” asked Jack in surprise.

Frank explained.

“Well,” said his chum consolingly, “a miss is as good as a mile, you know.”

“Nevertheless,” replied Frank, “the second might not be a miss. Keep your eyes open.”

“I’ll keep them open, never fear,” said Jack. “Now, you go to bed.”

“All right,” said Frank, and left his friend alone.