Naturally, Mr. Trenton was eager to know what we had accomplished and bombarded me with questions the moment I stepped foot in my apartments, which was not until late, for I had stopped at the office to attend to some pressing business first. I put him off, however, by saying that McKelvie was just getting his bearings and we'd have definite news when I heard from him again. I expected that he would call me up next day, but I received no word from him, so that I had plenty of time to speculate on the little I knew.

Personally, I was not sorry that Philip Darwin had failed, because I did not relish the idea of Ruth's inheriting his money, but I could not understand why McKelvie had disparaged Cunningham's motive in giving us this information. Not that I wanted to side with the man. I felt the same unreasonable antagonism that McKelvie evidently experienced toward him, but I wanted to be fair, and as far as I could see he was desirous of helping us as much as he could.

At any rate, motives for the crime, as far as Ruth was concerned, were valueless, since we knew of the existence of the secret entrance. What troubled me most was this point. Why should any sane man (I presume that the criminal was sane, if criminality is not another form of insanity) I repeat, why should any sane man shoot another one in the dark in the presence of a third person with the chances ten to one against his hitting the one at whom he aimed, and ten to one in favor of his being discovered? It was absurd on the face of it, yet it was just what had happened in the study that night, and twist it as I would I could make neither rhyme nor reason out of it. McKelvie had said the criminal was a clever man and clever criminals don't usually leave anything to chance, for only chance could have directed his aim in a room so dark that he could not possibly see his prospective victim!

Though I thought about it continually, this point was still a puzzle when McKelvie phoned me, early the second day after our visit to Riverside Drive, and asked me to meet him there at ten o'clock, but to tell no one where I was going. As I was in the habit of leaving for the office about eight I said nothing of my ultimate destination to Mr. Trenton, but I ordered Jenkins to be at the office as near nine-thirty as possible. I did not know whether McKelvie wanted him or not, and it was simpler to dismiss him than to send for him.

When we entered Darwin's study at ten o'clock sharp McKelvie was standing at one of the windows whistling. He greeted us with a smile and the remark, "Well, I'm all ready to tell you how the murder was committed."

"You have discovered something new?" I asked quickly.

"One or two things, but nothing bearing on my statement. I knew before I entered this room day before yesterday how it was done. For another that might seem impossible, but for me, no. It was simplicity itself."

I couldn't help smiling at this piece of conceit and catching my look he laughed good-humoredly.

"All great detectives—and I am one, according to my friend, Cunningham—are egotistical," he said.

"Is that the reason that Sherlock Holmes is an egotist, sir?" asked Jenkins suddenly.

"Undoubtedly; and why not, since he is the greatest of his kind. You see great detectives seldom fail, and so naturally they become—well—self-opinionated," returned McKelvie.

But I had not come there to discuss the failings of detectives, great or small, so I proceeded to dismount him from his hobby.

"You said you knew how the murder was done. So does anyone who reads the papers. The coroner's inquest made that fact plain," I said to get him started. I had learned already that he disliked having his statements belittled.

"The coroner's inquest!" he scoffed. "Haven't you the wit to see that the inquest was in the hands of the police from the start? Jones questioned Orton in the morning and then calmly used Graves and his jury as a vehicle for tightening the net in which Mrs. Darwin had become entangled. What chance then had the truth for even so much as lifting its head? I suppose the police explained to your satisfaction how the murderer shot so accurately in the dark?" he ended, cynically.

I smiled inwardly as I realized that I had drawn the very fire I wanted. Now I would have the answer to my puzzle.

"Well, how did he do it?" I asked, unruffled.

"He didn't. He shot Darwin while the lamp was lighted, like any right-minded person," he answered triumphantly. "By the way, Jenkins, I don't believe I'll need you to-day."

"Very well, sir."

I waited until Jenkins had gone and then I replied to McKelvie's statement. "What you have just remarked is utterly impossible," I retorted. "Ruth heard the shot before she saw the lamp spring into being, and she was speaking the truth."

He laughed. "Certainly, I am not disputing that point. I am merely making the assertion that the murderer shot his victim while the lamp, and for all I know, all the lights were lighted."

"But——"

"On second thoughts I don't believe I'll tell you. You might be as skeptical of my information as you were triumphant just now at having roused my ire," he answered laconically, and I knew that I had not deceived him long with my pretense of blockheadedness.

"I promise to believe anything you may say and swallow it all, hook, line and sinker," I pleaded.

"Well, perhaps under those circumstances—" he appeared to reflect, then said abruptly, "Would you call Dr. Haskins a man who knew his business?"

"Yes, decidedly so," I replied, surprised at the turn in the conversation.

"He remarked, if you remember, that Philip Darwin lived twenty minutes after the bullet had penetrated his lung, and yet he also agreed with the coroner's physician that Philip Darwin died at midnight or shortly thereafter. You yourself can testify that the shot was fired at midnight. How then do you account for the discrepancies in these various facts, for facts they are?"

My mind reverted to the inquest, and I heard again the pompous coroner's physician explaining Dr. Haskins' mistake, and I also recalled the young doctor's face, which certainly belied his apparent acquiescence with the other's statement. And suddenly I saw what McKelvie was driving at. Yet, how could it possibly be?

"You mean that he had already been shot when Ruth entered this room?" I said slowly, hardly daring to believe that which I uttered. It was so incredible, so seemingly impossible!

"Yes, just that." The words came with quiet conviction.

"But I heard no other shot, and Philip Darwin was alive at eleven-thirty!"

"Of course you heard no shot. We're dealing with a clever man, I tell you, and he wasn't advertising his actions," returned McKelvie, with that note of impatience in his voice which crept into it whenever I failed immediately to grasp the point. "I'll show you how it was done, so that no one could possibly have heard that shot, even if there had been someone listening at door or windows, which, of course, there was not."

He walked to the safe, and unlocked the door. Then he inserted his key in the back wall and ushered me into the secret room.

"In here," he said, "no noise, however great, could be heard without these walls. They are sound-proof, for I have tested them myself. I fired a pistol by means of a mechanism, and then listened in the hall for its explosion. I heard nothing. When I returned to this room the pistol had gone off, as was intended. So you can see that shooting his victim in here with the doors closed there was no chance that the shot would be heard by anyone in the house at the time."

I stared at him in astonishment. "But, McKelvie, Jones proved beyond the shadow of a doubt that Philip Darwin had just risen in his chair at the table when he was shot," I protested.

"Jones proved it!" he jeered. "Ye gods! Jones proved it! Of course he proved it. What else would you expect of Jones? Why do you suppose the murderer took the trouble to make those marks in the carpet except to fool the police?" he raged. "Certainly Jones proved it when it was put there for that purpose!"

"Granted," I said pacifically. "He shot Darwin in this secret room. Then what?"

McKelvie calmed down and resumed his story. "Then he proceeded to manufacture evidence. He carried his victim through the safe," returning to the study as he spoke and relocking the entrance, "placed him in that chair and arranged everything to look as though Philip Darwin had been writing, as indeed he had been when Orton came in at eleven-thirty. Then, satisfied that all was as perfect as he could make it, he turned off the light and waited."

"What for?"

"Mrs. Darwin, naturally."

"How on earth did he know she would come into the room? How could he possibly divine that I would urge her to get me that letter when I only spoke on impulse myself?"

McKelvie sighed. "I'm not omniscient. If I could tell you how he knew it, or why, I could tell you who committed the crime. I am only reconstructing what actually happened, for he was in the room at midnight, wasn't he, since he fired that second shot and lighted the lamp? And is it reasonable to suppose that it took him twenty minutes to shoot his victim and place him in that chair?"

I acquiesced, but not because I could see through the affair. It was growing more intricate with every step we took. "But why, man, why?" I persisted.

"Because he needed a scapegoat. It may be, of course, and probably is, the fact that he was about to leave when he heard Mrs. Darwin try the door, and that the idea then came to him to incriminate her."

"Why—that's monstrous!" I cried.

McKelvie shrugged. "When you are dealing with a murderer, his little ideas are apt to be rather outside the pale of civilized folk," he returned ironically. "By providing the police with a suspect he escaped their vigilance. Mrs. Darwin had the most motive for killing her husband; therefore, she made the best possible victim. But he figured without me. It's like a game of chess. He makes a move. I block him. At present it's 'check,' with all the advantage on his side and every prospect of the jury finding Mrs. Darwin guilty of the murder."

He had forgotten my presence and was talking to himself, his eyes grown dreamy as he gazed into the distance. At my exclamation, he passed a hand across his eyes, saying in a different tone, "I beg your pardon. I forgot in my interest in matching my wits against his, that to you Mrs. Darwin is more than a pawn in the game."

"McKelvie, surely you can't be serious," I implored him.

"I'm sorry to say that I am," he returned. "The prosecution has a very strong case, and we have nothing we can offer that refutes a single point that they can make." He moved away from the window, where he had been sitting for some little time, and began to pace the room in long, even strides.

"If only I knew where that second bullet had lodged itself! The physician declares there was only one wound and only one bullet; therefore, it's not in Darwin's body. Also, I have searched every square inch of this room—walls, ceiling, floor, carpet and furniture. There's not a trace, nor even the faintest shadow of a trace of that bullet!"

He shook his head despairingly, but I had hardly listened to his harangue. My mind had leaped to a sudden joyful conclusion.

"McKelvie," I cried, "we have evidence to refute their arguments! Let's go before the district attorney and tell him what we have learned and insist on his releasing Ruth at once!"

"What evidence do you refer to?" he inquired a bit coldly. "Do you take me for a mere calculating machine without any human feelings and consideration for others? Don't you suppose that if I had any valuable evidence I should have used it to advantage long ere this?"

"Why," I stammered, all the wind taken out of my sails, "what about the—the secret entrance?"

"As to that, it may or may not have been used upon that fatal night. We conjecture because we are proving Mrs. Darwin innocent, but we do not positively know anything about it," he put in imperturbably. "Mr. Darwin may have lost or misplaced his key."

"How do you account then for the lighting of the lamp from the safe?" I persisted.

"Again, we do not know it was so lighted. Often, if a connection is loose, a jar or shock will light the lamp of itself."

"But the shot in the dark?"

"Ah, the police don't believe for a second that the room was ever in darkness at any time. They believe that you and Mrs. Darwin concocted that bit of evidence."

"When?" I spluttered.

"You gave the wrong impression about Mrs. Darwin the night of the crime. They would argue collusion before their arrival."

"But, McKelvie, what about the actual time when Philip Darwin was killed, twenty minutes before Ruth ever set foot in the study?" I continued, exasperated by his skillful refutation of my arguments.

"On what do I base that conclusion?" he asked quietly.

"On Dr. Haskins' testimony."

"Exactly. And do you believe for a moment that the district attorney will give credence to a fact which Coroner Graves practically ruled out of his court?" he demanded.

But I was still determined to have my way, for I wanted to free Ruth above everything else. "There's the second shot to prove it," I said stubbornly.

He looked at me a moment with a strange smile, then he tapped his head significantly. "Pardon me," he said quizzically, as I flushed angrily, "I had forgotten you are in love and that lovers are never logical. Don't be angry with me and I'll show you what would happen if I approached Grenville with your last statement as a proof of my previous deductions. You have no experience in such matters, but, unfortunately, I know Grenville so very well."

McKelvie drew his mouth down in imitation of the district attorney, whose picture I had seen more than once in the paper, and then continued his exposition, mimicking Grenville's soft voice, as I suppose, whenever the part demanded it.

"When I had been ushered into his office he would adjust his glasses and listen with an air of great politeness to all I had to say. Then, when I was through he would smile, still politely, very, if a trifle sarcastically, and remark in his purring voice (the purr of the tiger before he shows his claws):

"'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!"

"And that proves?"

"Just what I told you before, that we are face to face with a far cleverer, more cold-blooded man than even I had given him credit for being!"