e was about to go to Mademoiselle Stangerson.
He waited till I was asleep, and my friend Sainclair was busy trying to
rouse me. Ten minutes after that Mademoiselle was calling out, "Murder!"

"How did you come to suspect Larsan?" asked the President.

"My pure reason pointed to him. That was why I watched him. But I
did not foresee the drugging. He is very cunning. Yes, my pure reason
pointed to him; but I required tangible proof so that my eyes could see
him as my pure reason saw him."

"What do you mean by your pure reason?"

"That power of one's mind which admits of no disturbing elements to
a conclusion. The day following the incident of 'the inexplicable
gallery,' I felt myself losing control of it. I had allowed myself to be
diverted by fallacious evidence; but I recovered and again took hold of
the right end. I satisfied myself that the murderer could not have left
the gallery, either naturally or supernaturally. I narrowed the field of
consideration to that small circle, so to speak. The murderer could
not be outside that circle. Now who was in it? There was, first, the
murderer. Then there were Daddy Jacques, Monsieur Stangerson, Frederic
Larsan, and myself. Five persons in all, counting in the murderer.
And yet, in the gallery, there were but four. Now since it had been
demonstrated to me that the fifth could not have escaped, it was evident
that one of the four present in the gallery must be a double--he must
be himself and the murderer also. Why had I not seen this before? Simply
because the phenomenon of the double personality had not occurred before
in this inquiry.

"Now who of the four persons in the gallery was both that person and the
assassin? I went over in my mind what I had seen. I had seen at one and
the same time, Monsieur Stangerson and the murderer, Daddy Jacques and
the murderer, myself and the murderer; so that the murderer, then, could
not be either Monsieur Stangerson, Daddy Jacques, or myself. Had I seen
Frederic Larsan and the murderer at the same time?--No!--Two seconds had
passed, during which I lost sight of the murderer; for, as I have noted
in my papers, he arrived two seconds before Monsieur Stangerson, Daddy
Jacques, and myself at the meeting-point of the two galleries. That
would have given Larsan time to go through the 'off-turning' gallery,
snatch off his false beard, return, and hurry with us as if, like us, in
pursuit of the murderer. I was sure now I had got hold of the r