ary to watch him narrowly, and note his
demeanour and his movements. If he is guilty he'll betray himself
sooner or later. Thorpe was foolish to take down that knife a second
time. The fellow might have seen him and had his suspicions aroused
thereby. That's the worst of police inquiries. They display so little
ingenuity. It is all method--method--method. Everything must be done
by rule. They appear to overlook the fact that a window in the
conservatory was undoubtedly left open," he added.

"Well?" I asked, noticing that he was gazing at me strangely, full in
the face.

"Well, has it not occurred to you that that window might have been
purposely left open?"

"You mean that the assassin entered and left by that window?"

"I mean to suggest that the murder might have been connived at by one
of the household, if the man we suspect were not the actual assassin
himself."

The theory was a curious one, but I saw that there were considerable
grounds for it. As in many suburban houses, the conservatory joined
the drawing-room, an unlocked glass door being between them. The
window that had been left unfastened was situated at the further end,
and being low down was in such a position that any intruder might
easily have entered and left. Therefore the suggestion appeared a
sound one--more especially so because the cook had most solemnly
declared that she had fastened it securely before going up to bed.

In that case someone must have crept down and unfastened it after the
woman had retired, and done so with the object of assisting the
assassin.

But Ambler Jevons was not a man to remain idle for a single moment
when once he became interested in a mystery. To his keen perception
and calm logical reasoning had been due the solution of "The
Mornington Crescent Mystery," which, as all readers of this narrative
will remember, for six months utterly perplexed Scotland Yard; while
in a dozen other notable cases his discoveries had placed the police
on the scent of the guilty person. Somehow he seemed to possess a
peculiar facility in the solving of enigmas. At ordinary times he
struck one as a rather careless, easy-going man, who drifted on
through life, tasting and dealing in tea, with regular attendance at
Mark Lane each day. Sometimes he wore a pair of cheap pince-nez, the
frames of which were rusty, but these he seldom assumed unless he was
what he termed "at work." He was at work now, and therefore had stuck
the pince-ne