Von Hauptwald was not far wrong in his remarks, for the instrument he had enabled him to flash a message to a confederate without having to be in possession of a lamp. The flash was obtained from any distant and visible light by means of a complicated system of mirrors. The reflected rays could then be projected in any desired direction so as to be quite invisible except on a certain bearing. It was one of the carefully-thought-out plans adopted by the German Government to permit its spies to communicate with their submarines without running any great risk of detection.
"It's two hours to sunset," remarked the doctor; "three before we commence operations. I would suggest that we adjourn to the cave and partake of refreshment. You see, I have not omitted to make suitable provision."
"Very good!" agreed von Ruhle; "but I only wish I had a waterproof. The rain is most annoying."
Arm-in-arm the two men left the building, and presently disappeared from view behind a slight rise in the ground.
"I say!" exclaimed Ross; "we've tumbled on something this time. Fancy Ramblethorne a rotten German spy. I always thought he was a rattling good chap."
"Evidently he isn't," rejoined Vernon. "But the point is: what do you propose to do? It's beastly wet here."
"It is, now I come to think of it," agreed his chum. "The fact is, that until you mentioned it I was hardly aware that it was raining. We'll discuss this knotty point."
"I vote we make tracks for the boat," suggested Haye. "The tide must be rising by this time. We can then slip off and raise the alarm."
Ross shook his head.
"No go," he decided. "We might get nabbed ourselves. Besides, who would be able to lay these chaps by the heels? There's only that motor-boat chap at Penydwick Cove, and he's precious little use. There are no soldiers nearer than at St. Bedal. I propose we hang on here. There's a snug, sheltered hole in these ruins, just big enough for us to lie hidden. Then we stand a good chance of hearing more of the conversation between those beggars."