like boxes of cigarettes.

"Yes. I see!" he exclaimed as I opened one. "Those are the detonators, filled with fulminate of mercury."

"Let us pass!" cried both the spies.

"Not before you are searched shall you leave this house!" was the quick reply. "If you resist, I shall fire into one of those boxes of detonators, and blow you to atoms."

"And yourselves also!" remarked Klauber, his face pale as death.

"It will at least prevent our secrets falling into your hands, and at the same time bring the truth home to the British Government!" was my friend's unwavering answer.

Next moment both men made a dash towards the door, but I had drawn my weapon and was upon my guard. There was a flash, followed by a deafening report, as Ray fired at the box, aiming wide on purpose.

Then the two spies, seeing that they had to deal with a man who was a patriot to his heart's core, realised that their game was up.

Sullenly Scholtz put down his weapon, and I searched both men.

From the pocket of the exemplary waiter I drew forth a rough plan, together with some scribbled notes in German, which afterwards proved to be a description of the forts on Inchkeith, while from the pocket of Scholtz I secured the tracing he had stolen from Rosyth.

Then we allowed both the secret agents of the Kaiser to pass out, much to the consternation and alarm of the deaf old Scotchwoman, who had, at their request, posed as the occupier of the cottage, but who, in perfect ignorance of what was in progress, had acted as their housekeeper.

A swift examination of the premises revealed no trace of Vera. But we found in the cellar below the room where we had found the spies a great store of gun-cotton and other high explosives of German manufacture, intended for the wrecking of the bridge; while in an old battered portmanteau in one of the upstairs rooms we also found, all ready for conveyance to Germany, a quantity of prints from the photographic negatives in the room below—photographs of nearly the whole of the plans of Rosyth, and more especially of its proposed forts—which the men had been in the habit of abstracting at night and replacing in the safe before dawn.

Ray Raymond was in active search of something else besides, and at length discovered what he sought—two German military telegraph instruments, together with a complete and very ingenious arrangement for the tapping of wire.

"By Jove!" exclaimed my friend, who took a keen interest in all things electrical. "This will now come in very handy!"

And on going outside to the telegraph pole against the wall, he clambered up it and attached wires to two of the insulators. Then descending, he screwed a little brass box upon it into those same three holes in the black wood which had attracted him on the night of our arrival, and a moment later began manipulating the key.

"Good!" he exclaimed at last. "I've picked up Inverkeithing, and asked them to send the police over at once. We mustn't leave the place and risk the spies returning for any of their paraphernalia. The disappearance of Vera, however, worries me. I sent her here with a note purporting to come from the chief of the German Secret Service in England, Hermann Hartmann; but she has vanished, and we must, as soon as the police arrive, go in search of her."

So completely had we unmasked the spies that I stood puzzled and amazed.

Ray, noticing my attitude, made explanation.

"Several of my surmises in this case proved entirely correct," he said. "My first suspicion was aroused that if spies were about, they would probably prepare for tapping the telegraph lines, and, as you know, I soon discovered evidence of it. Then those staples in the foundations of the bridge gave me a further clue to the work in progress, a suspicion greatly strengthened by the signal light shown by the man Klauber. The two men who held the safe keys being members of the Golf Club aroused a theory which proved the correct one, and on tracing back the career of the waiter I made a remarkable discovery which left no doubt as to his real profession. It seems that while employed at the Café de l'Europe in London, he lodged at the house of Mrs. Jephson, in Shepherd's Bush, and became extremely friendly with the widow's son. Now you'll remember that a few days before the poor fellow's death he was absent mysteriously, and on his return he told his mother in confidence that there would shortly be something in the papers about himself. Well, the truth is now quite plain. During his absence he evidently came up here. Young Jephson, who knew German, had found out that his German friend was a spy, and had no doubt secured the document afterwards found upon him as evidence. Klauber was ignorant of this, though he suspected that his secret was out. In deadly fear of exposure, he then plotted to silence the young Englishman, inducing him to walk along the towing-path between Hammersmith and Barnes, where he no doubt pushed him into the river. Indeed, I have found a witness who saw the two men together in King Street, Hammersmith, on the evening of the poor fellow's disappearance. The plan which Reitmeyer saw is, I find, fortunately one of the discarded ones."

"Extraordinary!" I declared, absorbed by what he had related. "But while you've wrested from Germany the secrets of some of our most important defences, you have, my dear Ray, temporarily lost the woman you love!"

"My first duty, Jack, is to my King and my country," he declared, sitting on the edge of the table in the spies' photographic studio. "I have tried to perform it to-night, and have, fortunately, exposed the German activity in our midst. When the police arrive to view this spies' nest, we must at once search for her who is always my confidante, and to whose woman's wits and foresight this success is in no small measure due."

CHAPTER II

THE SECRET OF THE SILENT SUBMARINE

"It's a most mysterious affair, no doubt," I remarked. "Has anything further been discovered?"

"Yes, Jack," replied my friend Ray Raymond, rolling a fresh cigarette between his fingers. "On investigation, the mystery grows more complicated, more remarkable, and—for us—much more interesting."

We were seated together in our dismal chambers in New Stone Buildings, Lincoln's Inn, one wet afternoon about six weeks after the Forth Bridge affair. With us, lolling in the shabby old easy chair beside the fire, sat Vera Vallance, in a big black hat, with her muff and coat thrown aside. Her disappearance at North Queensferry had been of only brief duration, for we had discovered her hiding at the bottom of the long garden, close to the water's edge, watching the landing of two small boxes from a boat. It appeared that the two men, Scholtz and Klauber, on receipt of the note purporting to come from their director, Hermann Hartmann, in London, had asked her to wait in an adjoining room while they wrote a reply. But from there she had slipped out, and concealed herself in the garden to wait and watch.

Half an hour ago she had come to my gloomy chambers with her fiancé, in order, as he explained, to consult with us. She was at present on a visit to her married sister who lived in Argyll Road, near Kensington High Street, hence they were daily in each other's company.

"You see, Jack, very little has been allowed to leak out to the papers," Ray exclaimed as he lit his cigarette and took up a position with his back to the fire. "As soon as I read of the discovery I ran down to Scotland Yard, saw Evans, and explained my theory. He was inclined to agree with me, and at once gave orders that no facts were to be given to the Press. Upon complete secrecy, our success now depends."

"I only know what I've