“I have ceased visiting my friend’s apartment in upper New York.  If you ever want me again, you will find me amongst my books.  If my invention halts and other interests stale, you have furnished me this day with a problem which cannot fail to give continual occupation to my energies.  If I succeed in solving it first, I shall be happy to share my knowledge with you.  Till then, trust the laws of nature.  No man when once on the outside of a door can button it on the inside, nor could any one without the gift of complete invisibility, make a leap of over fifteen feet from the sill of a fourth story window on to an adjacent fire escape, without attracting the attention of some of the many children playing down below.”

He was half-way out the door, but his name quickly spoken by the Inspector drew him back.

“Anything more?” he asked.

The Inspector smiled.

“You are a man of considerable analytic power, as I take it, Mr. Brotherson.  You must have decided long ago how this woman died.”

“Is that a question, Inspector?”

“You may take it as such.”

“Then I will allow myself to say that there is but one common-sense view to take of the matter.  Miss Challoner’s death was due to suicide; so was that of the washerwoman.  But there I stop.  As for the means—­the motive—­such mysteries may be within your province but they are totally outside mine!  God help us all!  The world is full of misery.  Again I wish you good-day.”

The air seemed to have lost its vitality and the sun its sparkle when he was gone.

“Now, what do you think, Gryce?”

The old man rose and came out of his corner.

“This:  that I’m up against the hardest proposition of my lifetime.  Nothing in the man’s appearance or manner evinces guilt, yet I believe him guilty.  I must.  Not to, is to strain probability to the point of breakage.  But how to reach him is a problem and one of no ordinary nature.  Years ago, when I was but little older than Sweetwater, I had just such a conviction concerning a certain man against whom I had even less to work on than we have here.  A murder had been committed by an envenomed spring contained in a toy puzzle.  I worked upon the conscience of the suspect in that case, by bringing constantly before his eyes a facsimile of that spring.  It met him in the folded napkin which he opened at his restaurant dinner.  He stumbled upon it in the street, and found it lying amongst his papers at home.  I gave him no relief and finally he succumbed.  He had been almost driven mad by remorse.  But this man has no conscience.  If he is not innocent as the day, he’s as hard as unquarried marble.  He might be confronted with reminders of his crime at every turn without weakening or showing by loss of appetite or interrupted sleep any effect upon his nerves.  That’s my opinion of the gentleman.  He is either that, or a man of uncommon force and self-restraint.”