ning that our agents would be so foolish as to
start blinking with a lamp; yet they allow these lighthouses to work as
usual, and obligingly enable us to communicate to our hearts' content."

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."

"Three hours more, remember."

"Yes, I know. In the meanwhile we might slip down to Main Beach Cove.
There's plenty of cover amongst the rocks."

"What for?" asked Vernon.

"To see what thes