uhle.

"On the contrary, it is just the very thing," replied the doctor. "It
is not thick enough to be dangerous, but the rain is just sufficient to
assist in the screening of U75. Do not think of your personal comfort,
my dear von Ruhle, when urgent work for the Fatherland has to be
undertaken."

For another half-hour the two men paced the grass-grown stones. Their
choice of St. Mena's Island as a secret signalling station was an
excellent one. It was isolated, and, being slightly greater in
elevation than the cliffs of the mainland in the immediate vicinity,
would effectually screen any ray of light sent landwards from the
expected German submarine. Thus all danger of the narrow gleam of
reflected light being detected by the none too smart members of the
coast patrol was entirely obviated.

"Time!" exclaimed the doctor, consulting the luminous face of his watch.

Dexterously, and without disturbing the position of the instrument, von
Ruhle whipped off the covering. Although there were no visible signs
that anything was taking place, both men knew that a beam of light,
reflected from the distant lighthouse on Black Bull Head, was being
directed seawards.

In silence the two men peered through the driving rain, von Ruhle
making use of a pair of powerful night-glasses.

Suddenly, after an interval of almost five minutes, a faint pin-prick
of light flickered from the surface of the sea.

Instantly Ramblethorne stepped a dozen paces to the right.

"I can see nothing from here," he announced in a low voice. "Can you?"

"Yes," replied his companion.

"Good: that's friend Schwalbe."

The doctor was right. From the deck of the unterseeboot a signalling
apparatus similar to that employed by the spies was in use. By an
ingenious automatic arrangement it projected a beam of light, derived
from the same sources as that on St. Mena's Island, rigidly in a fixed
direction, regardless of the "lift" of the submarine under the action
of the waves.

For several minutes a rapid exchange of signals was maintained; then
the two spies, folding up their apparatus, walked rapidly towards Main
Beach Cove.

They had not long to wait before the faint sound of oars was borne to
their ears.

"Himmel! They have arrived already," exclaimed von Ruhle.

"So it appears," replied Ramblethorne dryly. "I pride myself that I
have exceptionally good eyesight, but I fail to see her. The neutral
colour of the submarine is indeed