“I don’t blame you for adopting a policy of partial concealment,” said the Chief Inspector, spryly.  “You are not the first, and you certainly will not be the last witness from whom the police have to drag the facts.  Now that we have reached more intimate terms, can you help by describing this stranger?”

Theydon complied at once.  He drew just such a general sketch of Forbes as a skilled observer of men might be expected to formulate after one direct glance close at hand, supplemented by a view into a lamp-lit street from a second-storey window on a rainy night.

“So far, so good,” said Winter.  “You have contrived to fill in several details lacking in the description supplied by a policeman who chanced to be standing at the corner when Mrs. Lester’s visitor posted a letter.  Did you notice that?”

“Yes.  Indeed, I believed that, whether intentionally or not, he held an open umbrella at an angle which prevented the constable from seeing his face.”

“In fact, it’s marvellous what you really do know when your memory is jogged,” snapped Furneaux.

Theydon did not resent the sarcasm.  He smiled candidly into the little detective’s eyes.

“I suppose I deserve that,” he said meekly.

“Why did you hide your knowledge of Mrs. Lester’s visitor from your man Bates?”

“I was rather ashamed of the subterfuge adopted in order to get him out of the room while I opened the window the first time.”

“That was understandable last night, but I fail to follow your reasoning for a policy of silence when we told you at Waterloo that Mrs. Lester had been killed.”

“I was utterly taken aback by your news.  I wanted time to think.  I never meant to hide any material fact at this interview.”

“You have contrived to delay and hamper our inquiry for twelve hours—­ twenty-four in reality.  I can’t make you out, Mr. Theydon.  You would never have said a word about your very accurate acquaintance with this mysterious stranger’s appearance had not last night’s rainstorm left its legible record on your clothes.  Do you now vouch for it that the man was completely unknown to you?”

“You are pleased to be severe, Mr. Furneaux, but, having placed myself in a false position, I must accept your strictures.  I assure you, on my honor, that the man I saw was an absolute stranger.”

Happily, Theydon was under no compulsion to choose his words.  He met the detective’s searching gaze unflinchingly.  Fate, after terrifying him, had been kind.  If Furneaux had expressed himself differently—­ if, for instance, he had said:  “Had you ever before seen the man?” or “Have you now any reason for believing that you know his name?”—­ he would have forced Theydon’s hand in a way he was far from suspecting.

“It may surprise you to hear,” piped the shrill, cracked voice, “that there are dozens of policemen walking about London who would arrest you on suspicion had you treated them as you have treated us.”