"'Of course, since only one shot was fired from Mr. Darwin's pistol, you have brought with you the weapon that produced the second shot?'
"I would have to acknowledge that I not only had no such weapon, but not even the prospect of finding it.
"'No? Then, of course,' with a still deeper purr, 'you have brought me the bullet itself?'
"'Well, no,' I would answer sheepishly, 'I haven't even got that.'
"'What! No bullet either? Dear, dear, Mr. McKelvie, you really are a genius in your line. And you would actually have me credit the evidence of a chimera, a hypothetical revolver that fires a shot that leaves no trace——'"
Here McKelvie broke off abruptly and banged his fist against his forehead. "Stupid, stupid. Oh, that someone would write me down an ass!"
"What's the trouble, now?" I asked. "I thought you were doing very well."
"As regards Grenville? Well, I'm glad you realize that we couldn't prove anything with mere deduction unsubstantiated by facts, for any clever prosecutor could knock our evidence into a cocked hat. No, I was referring to something else," he returned, gazing somberly before him with a look akin to horror in his eyes.
"What is it?" I demanded.
He shook off whatever was troubling him and replied in a self-contemptuous tone, "Nothing, except that I must be getting old. I have actually allowed myself to ape that pompous idiot of a coroner's physician, and have thus been guilty of the worst crime in the decalogue of a detective. I have been fitting the facts to my theory instead of fitting my theory to the facts!"