They reached at length a small dilapidated square. The houses there had a sinister air in the midst of their dirt and decay. Boris looked round, and Tommy drew back into the shelter of a friendly porch. The place was almost deserted. It was a cul-de-sac, and consequently no traffic passed that way. The stealthy way the other had looked round stimulated Tommy’s imagination. From the shelter of the doorway he watched him go up the steps of a particularly evil-looking house and rap sharply, with a peculiar rhythm, on the door. It was opened promptly, he said a word or two to the doorkeeper, then passed inside. The door was shut to again.

It was at this juncture that Tommy lost his head. What he ought to have done, what any sane man would have done, was to remain patiently where he was and wait for his man to come out again. What he did do was entirely foreign to the sober common sense which was, as a rule, his leading characteristic. Something, as he expressed it, seemed to snap in his brain. Without a moment’s pause for reflection he, too, went up the steps, and reproduced as far as he was able the peculiar knock.