T. B. Smith sat alone in his office in Scotland Yard. Outside, the Embankment, the river, even the bulk of the Houses of Parliament were blotted out by the dense fog. For two days London had lain under the pall, and if the weather experts might be relied upon, yet another two days of fog was to be expected. The cheery room, with its polished oak panelling and the chaste elegance of its electroliers, offered every inducement to a lover of comfort to linger. The fire glowed bright and red in the tiled fireplace, a silver clock on the mantelpiece ticked musically, and at his hand was a white-covered tray with a tiny silver teapot, and the paraphernalia necessary for preparing his meal--that strange tea-supper which was one of T. B. Smith's eccentricities. He glanced at the clock; the hands pointed to twenty-five minutes past one. He pressed a little button let into the side of the desk, and a few seconds later there was a gentle tap at the door, and a helmetless constable appeared. "Go to the record room and get me"--he consulted a slip of paper on the desk--"Number G 7941." The man withdrew noiselessly, and T. B. Smith poured out a cup of tea for himself. There was a thoughtful line on his broad forehead, a look of unaccustomed worry on the handsome face, tanned with the suns of Southern France. He had come back from his holiday to a task which required the genius of a superman. He had to establish the identity of the greatest swindler of modern times, Montague Fallock. And now another reason existed for his search. To Montague Fallock, or his agent, must be ascribed the death of two men found in Brakely Square the night before. No man had seen Montague; there was no photograph to assist the army of detectives who were seeking him. His agents had been arrested and interrogated, but they were but the agents of agents. The man himself was invisible. He stood behind a steel network of banks and lawyers and anonymities, unreachable. The constable returned, bearing under his arm a little black leather envelope, and, depositing it on the desk of the Assistant Commissioner, withdrew. T. B. opened the envelope and removed three neat packages tied with red tape. He unfastened one of these and laid three cards before him. They were three photographic enlargements of a finger print. It did not need the eye of an expert to see they were of the same finger, though it was obvious that they had been made under different circumstances. T. B. compared them with a smaller photograph he had taken from his pocket. Yes, there was no doubt about it. The four pictures, secured by a delicate process from the almost invisible print on the latest letter of the blackmailer, proved beyond any doubt the identity of Lady Dex's correspondent. He rang the bell again and the constable appeared in the doorway. "Is Mr. Ela in his office?" "Yes, sir. He's been taking information about that Dock case."