He closed the volume but held it on his lap.
“There, unquestionably, is where Ada got the suggestion for Rex’s murder. She and Rex had probably discovered the hidden passageway between their rooms years ago. I imagine that as children—they were about the same age, don’t y’ know—they used it as a secret means of correspondence. This would account for the name by which they both knew it—‘our private mailbox.’ And, given this knowledge between Ada and Rex, the method of the murder becomes perfectly clear. Tonight I found an old-fashioned bootjack in Ada’s clothes-closet—probably taken from Tobias’s library. Its width, overall, was just six inches, and it was a little less than two feet long—it fitted perfectly into the communicating cupboard. Ada, following Gross’s diagram, pressed the handle of the gun tightly between the tapering claws of the bootjack, which would have held it like a vise; then tied a string to the trigger, and attached the other end to the inside of Rex’s panel, so that when the panel was opened wide the revolver, being on a hair-trigger, would discharge straight along the shaft and inevitably kill anyone looking into the opening. When Rex fell with a bullet in his forehead the panel flapped back into place on its spring hinge; and a second later there was no visible evidence whatever pointing to the origin of the shot. And here we also have the explanation for Rex’s calm expression of unawareness. When Ada returned with us from the District Attorney’s office, she went directly to her room, removed the gun and the bootjack, hid them in her closet, and came down to the drawing-room to report the foot-tracks on her carpet—foot-tracks she herself had made before leaving the house. It was just before she came downstairs, by the way, that she stole the morphine and strychnine from Von Blon’s case.”
“But, my God, Vance!” said Markham. “Suppose her mechanism had failed to work. She would have been in for it then.”
“I hardly think so. If, by any remote chance, the trap had not operated or Rex had recovered, she could easily have put the blame on someone else. She had merely to say she had secreted the diagram in the chute and that this other person had prepared the trap later on. There would have been no proof of her having set the gun.”
“What about that diagram, sir?” asked Heath.
For answer Vance again took up the second volume of Gross and, opening it, extended it toward us. On the right-hand page were a number of curious line-drawings, which I reproduce here.
“There are the three stones, and the parrot, and the heart, and even your arrow, Sergeant. They’re all criminal graphic symbols; and Ada simply utilized them in her description. The story of her finding the paper in the hall was a pure fabrication, but she knew it would pique our curiosity. The truth is, I suspected the paper of being faked by someone, for it evidently contained the signs of several types of criminal, and the symbols were meaninglessly jumbled. I rather imagined it was a false clue deliberately placed in the hall for us to find—like the footprints; but I certainly didn’t suspect Ada of having made up the tale. Now, however, as I look back at the episode it strikes me as deuced queer that she shouldn’t have brought so apparently significant a paper to the office. Her failure to do so was neither logical nor reasonable; and I ought to have been suspicious. But—my word!—what was one illogical item more or less in such a mélange of inconsistencies? As it happened, her decoy worked beautifully, and gave her the opportunity to telephone Rex to look into the chute. But it didn’t really matter. If the scheme had fallen through that morning, it would have been successful later on. Ada was highly persevering.”
“You think then,” put in Markham, “that Rex really heard the shot in Ada’s room that first night, and confided in her?”
“Undoubtedly. That part of her story was true enough. I’m inclined to think that Rex heard the shot and had a vague idea Mrs. Greene had fired it. Being rather close to his mother temperamentally, he said nothing. Later he voiced his suspicions to Ada; and that confession gave her the idea for killing him—or,
