But neither ship nor human being was in sight.

“Might be one of the secret passageways used by the undersea boats,” Jack mused as he followed the curving line of the bay away from the ocean.

Presently he came to an abrupt halt at a break in the beach where the rolling sand dunes fell sheer away to the mouth of another waterway—–­this time a small stream that wound its way inland through a tortuous channel.  It was no more than two hundred feet across.

Jack realized this must be one of the canals with which the coast was known to be ribboned.  For a moment he stood in contemplation of the sight.  Now he was more than ever convinced that he had stumbled into a U-boat base.  The love of adventure gripped him and he determined to press on.

For the next ten minutes he threaded his way along the canal bank.  Suddenly, as he turned one of the snake-like twists in the course of the waterway, he found himself facing an old stone windmill that stood almost directly on the canal bank.  It was only a stone’s throw away.

Instinctively the boy threw himself upon the sandy loam.  There was not a sign of life about the abandoned structure.  In the peaceful days before the war it had, no doubt, been used by a Belgian farmer to water his fields.

But now Jack saw something that set his heart a-flutter.  From the dome-like crest of the windmill stretched a number of wires tautly drawn and leading away to some point beyond his range of view.  For a moment he contemplated the scene in silence with tingling nerves.  Satisfied at last that his presence was not yet known—–­if any human being was within the stone tower—–­he struggled up to a kneeling position and looked beyond the windmill.

What he saw now was a ramshackle farmhouse apparently deserted.  Up the side of the dilapidated building ran a great wide stone chimney that reared its head through the gabled roof like a leaning Tower of Pisa.  To this chimney led the wires from the windmill.

“A secret wireless station!” exclaimed Jack to himself.  “Undoubtedly in the hands of the Germans and being used by them in the direction of their U-boat fleets in the North Sea!” The boy’s pulses quickened at the thought.

Like an Indian on the trail he wormed his way forward until he came at last within ten feet of the windmill.  There was a window before him.  Slowly and cautiously he drew himself up to one side of the casement and then peered in through the latticed shutter.

At a table, on which was spread out the wireless apparatus, was a uniformed figure.  A helmet lay on the floor and the man’s head was bowed in his arms.  He was asleep.  A lantern hung on the wall toward the canal side and cast a dim flicker over the cramped interior of the place.  Stretching himself up on tiptoe, Jack surveyed the room, but noted not another person in sight.

Quick as a flash the lad withdrew from the window.  His plan of action now was clear.  He must get control of that wireless key and flash a message to the United States fleet in the North Sea!