Vance paused to light another cigarette, and after a moment’s thoughtful silence continued.

“We come now to the midnight visit to the Drukker house. That was a grim entr’acte forced on the murderer by the report of Mrs. Drukker’s scream. He feared the woman had seen Robin’s body thrown to the range; and when, on the morning of Sprigg’s murder, she had been in the yard and met him returning from the kill, he was more worried than ever that she would put two and two together. No wonder he tried to prevent our questioning her! And at the earliest opportunity he attempted to silence her for all time. He took the key from Belle Dillard’s hand-bag before the theatre that night, and replaced it the next morning. He sent Pyne and Beedle to bed early; and at half past ten Drukker complained of fatigue and went home. At midnight he figured that the coast was clear for his grisly visit. His taking the black bishop as a symbolic signature to the contemplated murder was probably suggested by the chess discussion between Pardee and Drukker. Then again, it was Arnesson’s chessman, and I even suspect him of telling us of the chess discussion to call attention to Arnesson’s chess set in case the black bishop should fall into our hands.”

“Do you think he had any idea of involving Pardee at that time?”

“Oh, no. He was genuinely surprised when Arnesson’s analysis of the Pardee-Rubinstein game revealed the fact that the bishop had long been Pardee’s nemesis. . . . And you were undoubtedly right about Pardee’s reaction to my mention of the black bishop the next day. The poor chap thought I was deliberately ridiculing him as a result of his defeat at Rubinstein’s hands. . . .”

Vance leaned over and tapped the ashes from his cigarette.

“Too bad,” he murmured regretfully. “I owe him an apology, don’t y’ know.” He shrugged his shoulders slightly, and, settling back in his chair, took up his narrative. “The professor got his idea for Drukker’s murder from Mrs. Drukker herself. She expressed her imaginative fears to Belle Dillard, who repeated them at dinner that night; and the plan took shape. There were no complications to its execution. After dinner he went to the attic and typed the notes. Later he suggested a walk to Drukker, knowing Pardee wouldn’t remain long with Arnesson; and when he saw Pardee on the bridle path he of course knew Arnesson was alone. As soon as Pardee had walked away, he struck Drukker and tipped him over the wall. Immediately he took the little path to the Drive, crossed to 76th Street, and went to Drukker’s room, returning by the same route. The whole episode couldn’t have occupied more than ten minutes. Then he calmly walked past Emery and went home with Drukker’s note-book under his coat. . . .”

“But why,” interposed Markham, “if you were sure that Arnesson was innocent, did you make such a point of locating the key to the alley door? Only Arnesson could have used the alley on the night of Drukker’s death. Dillard and Pardee both went out by the front door.”

“I wasn’t interested in the key from the standpoint of Arnesson’s guilt. But if the key was gone, d’ ye see, it would have meant that some one had taken it in order to throw suspicion on Arnesson. How simple it would have been for Arnesson to slip down the alley after Pardee had gone, cross the Drive to the little path and attack Drukker after the professor had left him. . . . And, Markham, that is what we were supposed to think. It was, in fact, the obvious explanation of Drukker’s murder.”

“What I can’t get through my head, though,” complained Heath, “is why the old gent should have killed Pardee. That didn’t throw any suspicion on Arnesson, and it made it look like Pardee was guilty and had got disgusted and croaked himself.”

“That spurious suicide, Sergeant, was the professor’s most fantastic joke. It was at once ironical and contemptuous; for all during that comic interlude plans were being made for Arnesson’s destruction. And, of course, the fact that we possessed a plausible culprit had the great advantage of relaxing our watchfulness and causing the guards to be removed from the house. The murder, I imagine, was conceived rather spontaneously. The professor invented some excuse to accompany Pardee to the archery-room, where he had already closed the windows and drawn the shades. Then, perhaps pointing out an article in a magazine, he shot his unsuspecting guest through the temple, placed the gun in his hand, and, as a bit of sardonic humor, built the house of cards. On returning to the library he set up the chessmen to give the impression that Pardee had been brooding over the black bishop. . . .