Without hesitation the sub opened the door of the cabin adjoining his and entered quickly and silently. The place was in darkness. Whether it was tenanted or not he was unable to ascertain. Closing the door he stood stock-still and listened. He could hear no sound of a person breathing. For five minutes he waited, then began to grope until he found the edge of one of the bunks. The sleeping-place was empty. There were not even blankets and bedding. This looked promising. He continued his exploration, testing the remaining bunks in turn, until he was able to come to the happy decision that by sheer good luck he had lighted upon an empty cabin. The glass scuttle in the port-hole was closed, but there was no dead-light in position over the opening. In that case it would be too risky to switch on the light, until he had taken due precautions. The dead-light squeaked shrilly on its hinges as he drew it to. He wondered whether the watch on deck heard the sound. He waited again. There were many footsteps descending the companion. He could detect von Langer's guttural tones, discussing some matter with one of the other officers. "Dash it all!" ejaculated Denbigh, a cold perspiration standing out on his forehead. "What if I'm in that fellow's cabin?" The men stopped outside the cabin. They were evidently indulging in horse-play, for once a heavy body struck the wall with a thud, followed by a chorus of boisterous laughter. Then, to Denbigh's intense relief, the officers went along the passage. Once again he had been lucky. Reassured he switched on the light. The cabin was bare of furniture. In one corner lay a pile of books and a couple of sea-stained portmanteaux. Hanging from a coat-hook was an officer's sword-belt. It was mildewed; the stitching of the holster had burst, the buckle was green with verdigris. Attached to the belt was a small, circular leather case secured by a strap. Denbigh handled it gingerly. There was something hard inside. Curiosity prompted him to unbuckle the strap and open the case. Within was a pocket-compass. What was more, it was a spirit one and seemingly in good order. Without compunction the sub abstracted the compass and slipped it into his pocket. As he did so he was startled to hear a deep groan. It seemed to sound close to his ear. He wheeled abruptly and shot a glance in the direction of one of the bunks, thinking that he had made a mistake in deeming it untenanted. There was no one there. Again the groan was repeated. This time the sound seemed to come from the adjoining cabin--the one occupied by Pat O'Hara. A hole in the bulkhead attracted Denbigh's notice. It was the aperture drilled by the Germans when they made their ineffectual attempt to chloroform the three British officers.