“15, Berlin Square South, N.W.21” [he began]. “Dear Mr. Moss, Your name has been given me by a mutual friend, as one who can be relied on as a dealer in second-hand cars. I am told that you can usually get hold of something to suit anyone’s requirements. Well, what I want is an Austin or Morris, about twelve horse-power, not older than 1934, price not above £75. Do you think that you can get hold of something for me? If you can, drive it around here this afternoon, as I am in rather a hurry to get fixed up, as I have to go on an important journey very shortly. If you cannot lay your hands on either of these, please bring along anything that you have anywhere near it, as it is very urgent that I should get fixed up soon. Please come this afternoon, as it is not sure at what times I shall be in for the rest of the week. Yours sincerely, Michael Baron.”

“Well, what do you make of that, Inspector?” asked Moss.

“First of all,” was Shelley’s comment, “that Mr. Michael Baron was very anxious to get you out to—would it be Cricklewood?—this afternoon.”

“Yes, damn him!” returned Moss. “And his blasted address doesn’t exist.”

“Doesn’t it, now?” Shelley positively beamed at him. “That is indeed very gratifying.”

“Gratifying, do you call it?” Moss objected. “I call it damned annoying. I went out there this afternoon, and spent hours looking for the blasted place. There’s a Berlin Square right enough. As a matter of fact I knew it, and had been there before. But it’s a square with only three sides, if you follow me. There’s a Berlin Square North, East, and West, but no South.”

Shelley positively purred. “Oh, very clever, very clever indeed,” he murmured. “Just near enough to a real address to keep you puzzled, you see, Mr. Moss. The whole affair carefully thought out.”

“Yes, but why?” asked Moss.

“Oh, that we shall find out in due course,” said Shelley calmly.

“You think so?”

“I’m sure of it.”

“Well, I’m glad of that, at any rate.”

“In the meantime, Mr. Moss, I’d like to perform a little experiment,” announced Shelley.

Moss looked alarmed. “Experiment?” he asked.

“Yes. I’d like to examine this letter for finger-prints. It’s postmarked ‘N.W.21,’ I see, so the man took the trouble to go out there to post it.” Shelley scribbled a note on a piece of paper, and then handed it to Cunningham, together with the letter.

“Take this to the finger-print department, Sergeant,” he said, “and ask them if they can identify any of the prints on it with anyone in our records. This isn’t a novice, and may well be due to an old hand at the game. I don’t suppose he’s left any prints, but the best people go astray at times.”