straight along the shaft and inevitably kill any one 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 down-stairs, 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 some one 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
