Having carefully studied every detail of the quaint personality Polly felt more amiable.

“And yet,” she remarked kindly but authoritatively, “this article, in an otherwise well-informed journal, will tell you that, even within the last year, no fewer than six crimes have completely baffled the police, and the perpetrators of them are still at large.”

“Pardon me,” he said gently, “I never for a moment ventured to suggest that there were no mysteries to the police; I merely remarked that there were none where intelligence was brought to bear upon the investigation of crime.”

“Not even in the Fenchurch Street mystery.  I suppose,” she asked sarcastically.

“Least of all in the so-called Fenchurch Street mystery,” he replied quietly.

Now the Fenchurch Street mystery, as that extraordinary crime had popularly been called, had puzzled—­as Polly well knew—­the brains of every thinking man and woman for the last twelve months.  It had puzzled her not inconsiderably; she had been interested, fascinated; she had studied the case, formed her own theories, thought about it all often and often, had even written one or two letters to the Press on the subject—­suggesting, arguing, hinting at possibilities and probabilities, adducing proofs which other amateur detectives were equally ready to refute.  The attitude of that timid man in the corner, therefore, was peculiarly exasperating, and she retorted with sarcasm destined to completely annihilate her self-complacent interlocutor.

“What a pity it is, in that case, that you do not offer your priceless services to our misguided though well-meaning police.”

“Isn’t it?” he replied with perfect good-humour.  “Well, you know, for one thing I doubt if they would accept them; and in the second place my inclinations and my duty would—­were I to become an active member of the detective force—­nearly always be in direct conflict.  As often as not my sympathies go to the criminal who is clever and astute enough to lead our entire police force by the nose.

“I don’t know how much of the case you remember,” he went on quietly.  “It certainly, at first, began even to puzzle me.  On the 12th of last December a woman, poorly dressed, but with an unmistakable air of having seen better days, gave information at Scotland Yard of the disappearance of her husband, William Kershaw, of no occupation, and apparently of no fixed abode.  She was accompanied by a friend—­a fat, oily-looking German—­and between them they told a tale which set the police immediately on the move.

“It appears that on the 10th of December, at about three o’clock in the afternoon, Karl Mueller, the German, called on his friend, William Kershaw, for the purpose of collecting a small debt—­some ten pounds or so—­which the latter owed him.  On arriving at the squalid lodging in Charlotte Street, Fitzroy Square, he found William Kershaw in a wild state of excitement, and his wife in tears.  Mueller attempted to state the object of his visit, but Kershaw, with wild gestures, waved him aside, and—­in his own words—­flabbergasted him by asking him point-blank for another loan of two pounds, which sum, he declared, would be the means of a speedy fortune for himself and the friend who would help him in his need.