bush? It looks jolly fishy. Of course I've heard plenty of talk of German secret petrol-bases in Great Britain, but I never believed the tales. By smoke! I fancy I've stumbled upon one now. The first question is, how am I to find a way out without being seen?"

Resuming his cautious crawl, Mr. Greenwood penetrated into the recesses of the cave, keeping within touch of the rows of petrol-cans on his right. Contrary to his expectations, the floor was smooth, though tending to rise in the direction in which he was proceeding.

At about twenty yards from the hole through which he had tumbled, he remembered that he had left his tracks uncovered. No need to creep on all-fours now, for he had the irregular patch of light to guide him. Grasping the displaced bush, he replaced it in the opening, and chuckling to himself he again resumed his tour of exploration.

His spirits were rising rapidly. The love of adventure, that had lain dormant for years, was reasserting itself. Also he began to realise that he had now a chance of doing something definite for his country—a chance that hitherto had been denied him on account of his age.

He had quite forgotten the derelict mine. The fears that he had entertained on that score had been completely dispelled by the thought that he had lighted upon a discovery of real national importance—the existence of a secret base for hostile submarines.

For quite a hundred yards he groped his way. The darkness was so intense that it appeared to have weight—to press upon his eyes. The tunnel, too, had contracted, for by extending both his arms he could touch the enclosing walls. Once or twice he stood erect to relieve the aching muscles of his back. He could then just touch the roof, which, although of solid rock, was bone-dry.

Suddenly his forehead came in contact with a hard object. It was the bottommost step of a stout ladder. The steps extended from side to side, for the tunnel was still contracting. Further progress, except by the ladder, was impossible, since the wall of rock terminated a short distance beyond the base of the steps.

Mr. Greenwood examined his surroundings with great exactitude before attempting the ascent. Everything had to be performed by the sense of touch. The steps were of far greater thickness than the usual type of ladder, and were more apart. Apparently they had been constructed to bear very heavy weights, each one being strengthened by means of a circular iron bar on the underside.

"I'm half inclined to use a match," thought Mr. Greenwood. "It's risky, with all those petrol fumes about, but—— No, I won't; I'll make the best of it."

Slowly he ascended. It reminded him of an infant attempting to climb a staircase for the first time. The steps, in spite of their solidity, creaked under his weight. The sounds, intensified by the enclosed surroundings, added to the uncanniness of the mysterious cave.

At the eighth step he found a trap-door above his head. It was what he expected; but the question arose, what was on the other side? He had no desire to blunder into the presence of half a dozen desperadoes, who would doubtless have no scruples in knocking him over the head and toppling his corpse down the cliff.

Even as he was considering the best thing to be done, he heard footsteps overhead and a deep voice exclaiming, "Now, then, Max; let's get on with the business. It's quite time we showed the signal. Hand me yon crowbar and bear a hand to lift this trap. It's heavy."

CHAPTER IV

THE SECRET PETROL-DEPÔT

"No, I don't want to meet Max & Co.—at least, not just yet," soliloquised Mr. Greenwood as he hurriedly and silently descended to the floor of the tunnel. His first thought was to retrace his steps, scramble through the opening and lie at full length upon the outside ledge, until he realised that the mysterious frequenters of the cave would still be between him and freedom.

Then he remembered that there was a space between the foot of the ladder and the end of the tunnel. It was not at all likely that this would be examined.

With an agility that he did not think himself capable of, Mr. Greenwood crawled between two of the steps and crouched in his place of concealment.

Barely had he done so when the trap-door was raised. A flood of light streamed from above, although, fortunately, the flight of steps threw a strong shadow upon the recumbent form of Mr. Greenwood.

"You vos leave open der door?" inquired a guttural voice.

"Yes, Max," was the reply. "It's main heavy, and there's no call to exert ourselves to bustin'-point. No one'll come here after dark."

The speaker descended, holding an electric torch in his hand. He was a short, thick-set fellow, dressed in soiled velveteens. He looked a typical gamekeeper.

The person addressed as Max followed. He was a tall, fair-haired, broad-shouldered man of about thirty years of age. He wore a long overcoat and muffler, a hard felt hat, grey trousers and brown boots, the latter being almost hidden under a thick deposit of mud.

"I've got a rope further along," continued the short man. "When they answer our signals and send a boat, I'll lower you down. Only don't forget it's cash on the nail."

"Vot vos dat?" asked Max.

"The fifty pounds agreed upon. We'll signal at intervals, but don't be too jolly cocksure. They can't always be to time. If they show up afore four in the mornin', count yourself lucky."

The men, still talking, moved down the tunnel, until a bend, that Mr. Greenwood had passed without being aware of it, screened the light from the place where he lay concealed.

"Now or never," he thought.

Extricating himself from his cramped position, he scaled the ladder. Then, with his head almost level with the trap-door, he waited until his eyes grew accustomed to the blaze of light.

The opening was placed in the floor of a room—the kitchen of a small cottage, apparently. The two windows were heavily curtained. The door was secured, in addition to the massive lock, by a stout oaken beam resting in iron staples at either end. The furniture was scanty, consisting of a deal table, on which lay the remains of a meal and a large oil-lamp; three rush-bottomed chairs; a dresser, and a well-worn horse-hair couch. On one of the beams overhead were slung a couple of double-barrelled sporting guns. Opposite the door was another opening to a second room.

Mr. Greenwood's first impulse upon emerging from the tunnel was to slam the heavy trap-door and pile the furniture on top of it. But, he reflected, the men had a means of escape by the rope of which the short man had spoken. Moreover, they would raise the alarm and prevent the approach of the expected boat, which, more than likely, would put off from a German submarine.

No, he must make his escape without arousing suspicion. It would be an easy matter to unbar the door, but since he could not replace the cross-bar after he was outside, such a step would be unwise.

Throwing back the curtain he tried one of the windows. It was a latticed casement. With a little agility he could squeeze through, replace the curtain and trust to luck that the unsecured window might escape detection.

Two minutes later he was breathing the open air—a free man.

He looked about him. The night air blew cold. He had no idea of the direction of Auldhaig. For the time being his quest for the cruiser was out of the question.

Far away and at a considerably lower level two rows of lamps glimmered through the darkness. They were the anchor lights of the decoy boats of the fleet lying in Auldhaig Harbour. The town and the actual ships were shrouded in darkness, but every night numbers of small boats, each showing a white light, were moored at some distance from the fleet. At one time they might be placed half a dozen cables' lengths to the north'ard of the