as he fidgeted incessantly with a piece of string; his long,
lean, and trembling fingers tying and untying it into knots of wonderful
and complicated proportions.

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 o