"Yale lock!" he whispered impressively.
We followed him silently as he stole on tip-toe across the landing, and watched him as he stood for an instant with the key in his land looking gloatingly at the brass disc. We saw him softly apply the nose of the fluted key-blade to the crooked slit in the cylinder, and, as we watched, it slid noiselessly up to the shoulder. The detective looked round with a grin of triumph, and, silently withdrawing the key, stepped back to us.
"You've run him to earth, sir," he whispered, "but I don't think Mr. Fox is at home. He can't have got back yet."
"Why not?" asked Thorndyke.
Miller waved his hand towards the door. "Nothing has been disturbed," he replied. "There's not a mark on the paint. Now he hadn't got the key, and you can't pick a Yale lock. He'd have had to break in, and he hasn't broken in."
Thorndyke stepped up to the door and softly pushed in the flap of the letter-slit, through which he looked into the flat.
"There's no letter-box," said he. "My dear Miller, I would undertake to open that door in five minutes with a foot of wire and a bit of resined string."
Miller shook his head and grinned once more. "
