Fortune has a way of favoring the bold. The corporal and a marine were in the corridor behind Darrin. The ober-lieutenant’s special guard had been hurled aside.

Hearing the outcries, the other two marines in the cabin sprang toward the German officer. One of these von Bechtold tripped and sent sprawling; the other he struck in the chest, pushing him back.

Just an instant later von Bechtold went down on his back, all five of the marines doing their best to get at him in the same second. But the German had had time to knock the lid from a battery cell and to plunge the envelope into the liquid contained in the jar. Then the German was sent to the mat by his assailants.

Darrin, following, his whole thought on the envelope, plunged his right hand down into the fluid, gripping the package that had been snatched from him.

“Sulphuric acid!” he exclaimed, and made a quick dive for a lidded fire bucket that rested in a rack. The old-fashioned name for sulphuric acid is vitriol, and its powers in eating into human flesh are well known. Darrin’s left hand sent the lid of the bucket flying. Hand and envelope were thrust into the water with which, fortunately, the bucket was filled. When sulphuric acid in quantity is added to water heat is generated, but a small quantity of the acid may be washed from the flesh with water to good advantage if done instantly. After a brief washing of the hand Dave drew it out, patting it dry with a handkerchief. Thus the hand, though reddened, was saved from painful injury. The envelope he allowed to remain in the water for some moments.

“Von Bechtold, you are inclined to be a nuisance here,” Darrin said coolly. “I am going to direct these men to take you above.”

“I am helpless,” replied the German, sullenly, from the floor, where he now lay passive, two marines sitting on him ready to renew the struggle if he so desired.

“Take him above, you two men,” Darrin ordered, “and take especial pains to see that he doesn’t try to escape by jumping into the water.”

At this significant remark von Bechtold paled noticeably for a moment. Then his ruddy color came back. He got upon his feet with a resentful air but did not resist the marines who conducted him up to the deck.

Dave now drew out the envelope, which had become well soaked, and took out the enclosure, a single sheet. The writing at the top of the sheet was obliterated. Darrin did not read German fluently, but at the bottom of the sheet he found a few words and phrases that he was able to translate. Their meaning made him gasp.

“Danny-boy,” he murmured to his chum, “I want you to make quick work of transferring the prisoners to the ‘Logan.’ Keep back two of the German engineer crew, and send word to Ensign Phelps to come over on the launch’s next trip with two men of our engine-room force, and to bring along also six seamen and a petty officer. Phelps will take charge of this craft as prize officer.”

The submarine was soon cleared of her officers and crew. Ensign Phelps and his own men came over and took command. Two German engine-room men had been kept back to assist the Americans. On the last trip Darrin and Dalzell returned to the undersea boat and gave the order to Ensign Phelps to proceed on his way to the base port.

As soon as the prize with its captors was under way, Darrin went to the chart-room of the “Logan,” sent for the marine corporal, and ordered that Ober-Lieutenant von Bechtold be brought before him.

As the prisoner was ushered in Dave rose courteously, bowed and pointed to a chair.

“Be seated, if you please. Now, Herr Ober-Lieutenant, your second-in-command and your crew will be taken ashore as ordinary prisoners of war, and turned over to the British military prison authorities. Of course you are aware that your own imprisonment will take place under somewhat different circumstances.”

Von Bechtold, who had accepted the proffered chair, gazed stolidly at this American naval commander, who was several years younger than himself.

“I fear that I do not understand you,” the German replied.

“You soon will, for you speak excellent English,” Darrin returned, with a chilly smile. “Your English does not have exactly the Chicago accent, but it was good enough for your purposes. The Chicagoan speaks with a sort of sub-Bostonese accent, as perhaps you did not know. Your own English has rather the sound of Oxford or Cambridge University in England.”

Opening his eyes wide, and expressing bewilderment, the German begged:

“Will you be good enough to speak more explicitly?”

“Certainly,” Dave assented. “When you are turned over to the British military authorities it will be done with a card showing that you now give the name of von Bechtold——”

“Which is my right name,” interposed the German officer, tartly.

“And the card will also state that, a few days ago, you gave the name of Matthews.”

“Again you use that name of Matthews,” cried von Bechtold, impatiently. “May I ask why?”

“I will make it so clear,” Dave promised him, “that you would understand even though what I am about to say were not true. But it is true. A few days ago you met me at the hotel in port. You met also my executive officer, Mr. Dalzell. You introduced yourself to us as Matthews, claimed to be a buyer for a Chicago dry-goods house, and declared that your mission was to buy linen.”

“Not a word of truth in it,” declared von Bechtold, calmly, with a wave of his hand, as though to brush aside the charge.

“Unfortunately, quite true,” Dave went on, steadily. “You were there under an assumed name and claimed to be an American citizen. You exhibited an American passport; I have heard that your government has a printing office where such documents are turned out. You were there out of uniform. In other words, sir, your conduct on British soil, in civilian dress and under false colors, met with all the requirements of proof that you were there as a spy. It has long been known to the British, and to us, that German spies have abounded in Great Britain and that they obtained a good deal of information that we would rather German submarine commanders did not possess. So, Mr. von-Bechtold-Matthews, it will be my disagreeable duty to hand you over with the charge that you have been serving as a spy. Dalzell and I will be obliged to testify against you. I much fear that a British court-martial will condemn you to be shot.”

“What infamous lie is this that you are threatening to utter against me?” demanded the German officer, leaping to his feet.

“No lie at all, as you know quite well,” Dave went on. “I am sorry to have to bring you to this plight, von Bechtold, but you know that I cannot do otherwise.”

Gazing into the steady eyes of the young American naval officer von Bechtold realized the folly of further acting. Breathing hard, he dropped into a chair.

“It is not a fine thing that you propose to do to me,” he declared. “You do not know, of course, that I have five young children at home, who will need a father.”

“I did not know it,” Dave answered gently. “Yet I feel quite certain that some of the information you have gathered, when ashore in these parts, has resulted in the drowning at sea of a good many men who may have left behind even more than five children.”

“I feel that I am doomed,” shuddered the German, throwing a hand up over his eyes. “My five little children will not see their father again—not even when this war is over.”

“It is too bad,” Dave answered, “but I suppose, Herr Ober-Lieutenant, that it must be classed with the fortune of war. Now, as to the identity of the civilian who lies dead in a berth aboard your late command, it may be that, if you were ready to tell something about the reasons for his presence on board, and why he had in his possession this paper——”

Here Darrin spread out the wet sheet of paper that he had brought from the submarine.

“I can tell you nothing about either the civilian or that paper,” declared von Bechtold, doggedly.

“That is your own affair,” Darrin admitted. “I shall not make any attempt to force you.”

“You had better not!” declared the German, fiercely. “I can die, but I cannot betray my country. Yet have you no heart?—when I tell you about my five little children whom you would deny the privilege of ever seeing their father again?”

“If I were to suppress my report of your activities as a spy,” Darrin continued, “I would be guilty of betraying my country and my country’s allies. It would also be necessary for me to induce my subordinate officer to do the same thing. You will realize the impossibility of our doing such a thing. On the other hand, between now and the time that you are tried by court-martial you will have time to reflect upon whether you wish to try to save yourself from the death sentence by explaining to the British authorities the full meaning of what had been written on this sheet of paper and also the reasons for that civilian being aboard your craft. Then, by throwing yourself on the mercy of the court, you might escape the full penalty meted out to a spy.”

“I shall not do it,” declared von Bechtold, rising and drawing himself to his full height.

“Nor do I believe I could be induced to tell what I knew if I stood in your boots. Orderly!”

To the marine who entered Dave gave the order to summon the guard. Von Bechtold was taken back to the “Logan’s” brig, and locked in for absolutely safe keeping. Darrin went up to the bridge.

“Do you feel sorry for the fellow?” asked Dalzell, when he had heard an account of the interview.

“No more sorry than I do for any man who is down and out,” Dave replied, truthfully. “Now that he is captured and his spy work ended, I believe that ships on these waters will be much safer.”

“He will be just one Hun less, after a firing squad has finished with him,” Dan rejoined.

Dave nodded thoughtfully.

“War breeds savage ideas, doesn’t it?” demanded Danny Grin, with a shrug of his shoulders.

“Not breeds, but brings out,” answered Darrin.

They were nearing the coast now. Destroyers, patrol boats, drifters and mine-sweeping craft sighted the “Logan” and her prize, and the shrill whistles of these hunters of the sea testified to their joy over the capture.

Then the destroyer and her prize entered the port. Darrin brought his craft to anchorage, while the captured submarine was anchored not far away. The German prisoners were taken ashore under guard and turned over to the British authorities.

Ober-Lieutenant von Bechtold, under the charge of being a spy, was marched away under a special guard.

And then Dave made haste to present himself, with the half-destroyed sheet of paper in his pocket, before the flag lieutenant of Vice Admiral Speare.