Ten minutes later the boats were in the turmoil of the troubled water caused by the swirl of the tide over Thorbury Ledge. Had it been light enough for anyone standing on the headland to watch the two diminutive craft struggling through the broken water, he would doubtless have expected to see the frail cockle-shells founder under his eyes.

It was hazardous work, certainly; but by this time Derek had the utmost confidence in the seaworthiness of his two craft. Often hidden from each other by the intervening crests, the boats behaved wondrously; but the youthful officer in charge was relieved to know that wind and tide were in the same direction. Had it been otherwise things might have been different. From the headland it was now plain sailing, for in the gathering light the slender tower of the lighthouse at Fort Churst could be discerned, standing out clearly against the dark background of the well-wooded hills. In forty minutes both boats were passing through the narrow channel. Signals were exchanged with the batteries, and the welcome order to proceed was received.

It was now comparatively smooth water. The crews, recovering from their malady, were able to sit up and take nourishment in the shape of bread and bully beef. More, they began to take a lively interest in their surroundings, although the aspect of that land-locked stretch of water in war-time and in November was far different from what it had been previous to August, 1914, when the sea was dotted with the sails of countless yachts.

"Wonder if it will ever be the same again?" thought Derek. "One thing\'s fairly certain: we won\'t see the German Emperor afloat here, unless as a prisoner of war on a British battleship."

Over a vast observation minefield the boats glided serenely. Fifty feet beneath their keels were cylinders of powerful explosive that at the touch of an electrically-connected key ashore would blow a hostile ship to atoms. Farther on there were mechanical contact-mines, moored fathoms down so that a vessel of the deepest draught could pass unscathed but should a U-boat attempt to nose her way in by creeping just above the bottom of the sea, her fate would be swift and terrible.

"Keep a sharp look-out for the gateway," ordered Derek, as he placed a fresh man at the helm. "It\'s getting a bit misty, and we don\'t want to run full tilt against the boom."

The boats were now nearing the innermost line of anti-submarine defences of the western approach to the greatest naval harbour in the world. Right across the water-way was a triple line of massive wire hawsers, supported by barrels at frequent intervals. So much was visible; what was not visible was a wondrous complication of nets, explosive charges, and other effective anti-submarine defences. Britain\'s sure and safe shield was taking no undue risks with Fritz and all his evil works. To enable authorized vessels to pass, a gateway had been constructed. Between two large craft moored a cable\'s length apart there was a movable section of the barrier, and towards this the two motor-boats steered.

"Motor-boats ahoy!" hailed an officer from one of the guard-ships. "You are to proceed to Bull Roads and await further orders from the S.N.O."

Against this mandate there was no appeal. The word of the Senior Naval Officer was more than law. Doubtless it meant irritating and apparently needless delay, but, whatever the object of the order, it had to be put into effect without delay.

"Aye, aye, sir!" shouted Derek in reply. He knew perfectly well that non-compliance would result in a six-pounder shell fired across his bows, and almost immediately a salvo from the guardship\'s quick-firers.

"Port helm!" continued Daventry, addressing the coxswain. Round swung his boat; the one astern instantly followed suit, and a course was shaped for Bull Roads, an open anchorage barely two miles distant.

Arriving here the boats had orders to anchor, and for four long hours they rolled heavily in the tide-way. Naval patrol-boats of all sorts and sizes passed continually, but none appeared to pay the slightest attention to the two strangers within their gates. It was not until well into the afternoon that a patrol-boat eased down within a few feet of Derek\'s craft.

"You can proceed," announced the officer.

"Why have we been detained?" asked Derek, wondering at the bald announcement and the lack of explanation.

The sub-lieutenant R.N.R. shrugged his shoulders.

"Ask me another, old sport," he replied. "If you want to carry on do so at once, before the Old Man puts another stopper on you. Bon voyage!"

The motors were started up; foot by foot the chain cables were brought on board until the anchors, their palms smothered in blue, slimy clay, were hauled up and secured. Then, in the gathering twilight, the boats headed for their destination. By this time the mist had increased considerably. Visibility was a matter of a couple of hundred yards. It was bitterly cold, the air being raw and damp. "Verily," thought Derek, "motor-boating in November differs considerably from yachting in August."

At length the huge air-sheds of the Wagshot Station loomed up through the mist. Ordering half-speed, Derek brought his boat alongside the pier, and signalled to the second craft to lie up alongside him.

"Where are you from?" enquired a great-coated individual from the pier-head—the Officer of the Watch.

"From. Sableridge," replied Derek. "We\'ve come to take away a sea-plane."

"First I\'ve heard about it," rejoined the O.W. "You\'d better see the Adjutant. You\'re stopping here the night?"

"\'Fraid there\'s no option," replied Daventry.

"Right-o! Moor your craft out there. I\'ll send a duty-boat out to take off the crews."

"Out there" was a partially-protected anchorage, about a hundred yards from the pier. The boats pushed off and made for their appointed stations for the night, Derek taking particular care that each boat was properly moored with both anchor and kedge.

This done the crews were taken off. Visions of a hot meal first for his men and then for himself (for it is an unwritten law that officers must first provide for the comfort of their crews before "packing up" themselves) were rudely shattered when the Officer of the Watch appeared.

"I\'ve seen the Adjutant," he announced. "You\'ll have to take those boats across to Bumble Creek. They\'ll be............