"Ah! remember all the details, they were so admirable! the letter posted in Brighton by the cunning rogue to himself, the smashed desk, the broken pane of glass in his own house. The man Robertson on the watch, while Knopf himself in ragged clothing found his way into No. 26. If Constable D 21 had not appeared upon the scene that exciting comedy in the early morning would not have been enacted. As it was, in the supposed fight, Mr. Shipman's diamonds passed from the hands of the tramp into those of his accomplice. "Then, later on, Robertson, ill in bed, while his master was supposed to have returned--by the way, it never struck anybody that no one saw Mr. Knopf come home, though he surely would have driven up in a cab. Then the double part played by one man for the next two days. It certainly never struck either the police or the inspector. Remember they only saw Robertson when in bed with a streaming cold. But Knopf had to be got out of gaol as soon as possible; the dual _rôle_ could not have been kept up for long. Hence the story of the diamonds found in the garden of No. 22. The cunning rogues guessed that the usual plan would be acted upon, and the suspected thief allowed to visit the scene where his hoard lay hidden. "It had all been foreseen, and Robertson must have been constantly on the watch. The tramp stopped, mind you, in Phillimore Terrace for some moments, lighting a pipe. The accomplice, then, was fully on the alert; he slipped the bolts of the back garden gate. Five minutes later Knopf was in the house, in a hot bath, getting rid of the disguise of our friend the tramp. Remember that again here the detective did not actually see him. "The next morning Mr. Knopf, black hair and beard and all, was himself again. The whole trick lay in one simple art, which those two cunning rascals knew to absolute perfection, the art of impersonating one another. "They are brothers, presumably--twin brothers, I should say." "But Mr. Knopf--" suggested Polly. "Well, look in the Trades' Directory; you will see F. Knopf & Co., diamond merchants, of some City address. Ask about the firm among the trade; you will hear that it is firmly established on a sound financial basis. He! he! he! and it deserves to be," added the man in the corner, as, calling for the waitress, he received his ticket, and taking up his shabby hat, took himself and his bit of string rapidly out of the room. CHAPTER VII THE YORK MYSTERY The man in the corner looked quite cheerful that morning; he had had two glasses of milk and had even gone to the extravagance of an extra cheese-cake. Polly knew that he was itching to talk police and murders, for he cast furtive glances at her from time to time, produced a bit of string, tied and untied it into scores of complicated knots, and finally, bringing out his pocket-book, he placed two or three photographs before her. "Do you know who that is?" he asked, pointing to one of these.