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 excellent for night work."
They descended the sandy and shingly beach until further progress was barred by the lapping wavelets of the rising tide.
Through the mirk loomed up the outlines of a canvas collapsible boat crowded with men. At two lengths from the shore the rowers laid on their oars. One of the men gave vent to a low whistle resembling the call of a curlew.
"All clear," replied Ramblethorne.
The boat's keel rasped on the shingle. A cloaked figure in the stern-sheets made his way for'ard and leapt ashore.
"Herr von Hauptwald?" he asked.
"The same," replied the doctor. "And Kapitan Schwalbe?"
"The captain is still on board," replied the officer. "It is hard to resist the opportunity of getting ashore after being cooped up there for more than a fortnight. But the petrol?"
"We have not so much as we hoped to obtain," replied von Ruhle.
The Leutnant muttered an oath.
"And how is business?" asked Ramblethorne, with a view of distracting the officer's thoughts from the shortage of fuel.
The Leutnant muttered another oath.
"Bad!" he replied savagely. "Only one wretched little tramp steamer, which we fell in with about twenty miles from the Stacks. She gave us a run for our money, but we had her at last. Even then she tried to ram us. One has to be most cautious also. These accursed English have been far too active with their new-fangled contrivances. We called up U71 early this morning. She replied. Again at noon we called her, but there was no reply. U70 we have lost all touch with since Monday, yet she was under orders to assist in the blockade of the Bristol Channel until we, as senior unterseeboot, gave instructions to return to Wilhelmshaven."
"Lost, I suppose," remarked Ramblethorne.
The Leutnant had walked to a distance of nearly ten yards from his men, who were drawn up in military order awaiting their officer's commands.
He lowered his voice.
"Although I am sorry to say it," he declared, "I am afraid she has gone too. Our losses are not only serious—they are appalling. Submarine work is now a continual nightmare. We do our duty, but before long, if we are sufficiently fortunate to escape the toils that these English cast about us, we shall all be physical wrecks."
The man's agitation increased as he spoke. Obviously he was labouring under a severe strain.
"And this petrol?" he asked anxiously. "What quantity?"
Ramblethorne told him.
"Not enough," declared the Leutnant. "Himmel, it is not enough to get us round Cape Wrath. On board we have only sufficient for six hours' surface running, while our batteries are not far short of running down. You had better see the captain and explain."
Leaving von Ruhle to direct the seamen to the secret petrol store in the cave, Ramblethorne accompanied the Leutnant to the submarine.
The U75 was one of the latest type of Germany's submarines. Over three hundred feet in length, there was little about her in common with the accepted idea of under-water craft. Her deck ran in one continuous sweep for almost her entire length, and rose nearly six feet above the surface. The visible part of her sides was perpendicular, the bulging sections being entirely beneath the surface. Her conning-tower was surrounded by a platform as long as the navigation-bridge of a modern destroyer. The two periscopes were "housed", but two slender "wireless" masts gave the boat the appearance of a swift torpedo craft.
Acknowledging a salute from a burly quartermaster, Ramblethorne gained the deck, and was escorted aft by the Leutnant. Pacing the tapering platform was a broad-shouldered, fair-haired man of about thirty, although a carefully trimmed blonde beard made him look much older.
He lacked the natural elastic stride of the British naval officer. His movements resembled those of a thoroughly drilled soldier, yet ever and anon he would glance furtively in the direction of the open sea as if in constant dread of sudden and unknown peril.
"Greetings, Herr von Hauptwald!" he exclaimed, when the Leutnant had formally introduced his visitor. "You are well known to me by repute, but I doubt whether we have met before."
"I fancy so," rejoined the doctor. "Do you not remember that little affair in the Strauer Platz? Ah, I thought you would! But to come to the point. We have been unable to obtain the requisite quantity of petrol."
"Somehow I thought it," replied Kapitan Schwalbe. "How much have you?"
Ramblethorne told him.
"Enough, with what we have left on board, for only eight hundred miles run. It will not take us home, and we are under orders not to leave these waters before Friday next. We have been let down badly."
"I know that it is useless to express regrets," said Ramblethorne boldly. "I can only hope that other means of supplying the requisite fuel will be forthcoming. But here is another matter. We have had to secure two English lads, both sons of distinguished naval officers. Unfortunately they overheard a conversation between von Ruhle and myself. In the interests of the Secret Service it is absolutely necessary that they are kept out of the way for at least a couple of months. I am averse to doing them personal injury."
"Then what do you wish?" asked Kapitan Schwalbe.
"Take them on board with you. If possible, land them at a German port. If this be possible, you will realize that we have a strong tool to work with."
"I fail to understand," said the Kapitan of U75.
"They could be made good use of as hostages," resumed Ramblethorne. "If these English persist in talking about reprisals, we can hint that—well, it is unnecessary to go into details."
"I see," remarked Kapitan Schwalbe. "But if it is impossible to land them?"
"Then you must put them on board the first outward-bound tramp steamer you fall in with—provided she is bound for South American ports, or anywhere that will mean a long voyage."
"Very well," assented the submarine officer. "I quite understand your anxiety to get them out of the way."
"Temporarily, mind," added Ramblethorne.
"Precisely. Herr Rix," he exclaimed, addressing the Leutnant. "Take four men and go ashore. Von Ruhle will tell you where these English boys are; have them brought on board."
"One moment," interrupted Ramblethorne. "They came to the island in a boat. There is nothing unusual in that, I admit, but the fact remains that the boat is still lying in the cove next to this. You might order the men to set the boat adrift."
"Water-logged, and with sails set and the main-sheet made fast. Another deplorable accident. Ach! It shall be so."
Half an hour later Ross Trefusis and Vernon Haye, still unconscious under the action of the anaesthetic injection, were brought on board U75 and passed below. Their boat, lying on its beam-ends, was drifting slowly in the direction of Black Bull Head. Ramblethorne and von Ruhle, their work for the present done, were already on the way to the mainland.
Meanwhile, alarmed at the non-appearance of the young heir to Killigwent Hall and his guest, a party had set off to search St. Mena's Island.
Just as the boat's keel grounded on the beach of Half Tide Cove, the German submarine slipped quietly through the blurr of misty rain, and under cover of darkness headed towards the mouth of Bristol Channel.