rned, with a touch of bitterness, "he ought
to have known that I should not betray him."

"Even if one had told you of those three dreadful crimes that he had
committed, and that an innocent man was accused of the last one?"

She locked her hands together.

"Don't ask me," she cried. "I don't know what I should have done."

"He foresaw that problem," said Monsieur Dupont. "His sanity was, as you
have said, wonderful. But the sanity of madness is always
wonderful--that is why madmen are such superb criminals. It is only a
madman who can be really sane. Although I allowed him to see that I knew
already something of the truth, he never betrayed himself by even a
tremor. He had all the grand egotism of the born criminal. His disguise
was impenetrable. He was never sure how far my knowledge went, but not a
sign of anxiety did he ever show. We played a game of cross purposes. I
used him, under the pretense of requiring his assistance, to keep him by
my side, and in the hope that as he saw me draw nearer to him step by
step, he would break down. He, on his side, allowed himself to be used
in order to keep watch on my moves, and safeguard himself against them,
as he did in the case of Miss Masters. He dared not leave me. In all my
conversations with him, I placed him more and more at his wit's end to
know how much I really knew. As much from curiosity as from anything, I
instructed him to discover the secret of Mr. Copplestone's house, for I
was convinced that it did contain an interesting secret. He was quite
willing to make the attempt. It did not promise to lead me any nearer to
him. He little thought when he went--and I had little thought when I
sent him--that he was going to his own undoing."

"And my salvation," Copplestone added.

"There," said Monsieur Dupont, "it passes to you to enlighten me."

"First," returned Copplestone, "I should like to know what caused you to
be so positive, after being in my house only two or three hours, that
there was a secret in it."

"My instinct for the mysterious is seldom at fault," said Monsieur
Dupont. "Have you not observed how, by their characters, their habits,
and their desires, human beings draw to themselves certain events and
conditions of life? And it is equally true that houses draw to
themselves certain contents and certain kinds of inhabitants. If a house
is particularly adapted to contain a secret, in the course of time will
certainly contain one. By a few strokes