between the door and the casing. The point halted against the inner moulding, and the edge of the blade scraped upon the circular bolt. There was no question that the heavy oak casings and mouldings of the door were solid and well fitted, and that the bolt had been securely thrown from the inside. Heath, however, was still suspicious, and, grasping the door-knob, he tugged at it violently. But the door held firmly. At length he threw the bolt-handle to a vertical position and opened the door. Vance was standing in the court, placidly smoking and inspecting the brickwork of the alley wall.
"I say, Markham," he remarked, "here's a curious thing. This wall, d' ye know, must be very old. It wasn't built in these latter days of breathless efficiency. The beauty-loving mason who erected it laid the bricks in Flemish bond instead of the Running—or Stretcher—bond of our own restless age. And up there a bit"—he pointed toward the rear yard—"is a Rowlock and Checkerboard pattern. Very neat and very pretty—more pleasing even than the popular English Cross bond. And the mortar joints are all V-tooled. . . . Fancy!"
Markham was fuming.
"Damn it, Vance! I'm not building brick walls. What I want to know is how you got out here and left the door bolted on the inside."
"Oh, that!" Vance crushed out his cigarette and re-entered the building. "I merely made use of a bit of clever criminal mechanism. It's very simple, like all truly effective appliances—oh, simple beyond words. I blush at its simplicity. . . . Observe!"
He took from his pocket a tiny pair of tweezers
