A man by the name of Mackenzie, Durkin gathered from what he could hear of their talk, had been probing about the underground cable galleries for half a day, and had just strung a wire on which much seemed to depend. They stopped before a heavy oak-panelled door, on which MacNutt played a six-stroked tattoo. A key turned, and the next moment a middle-aged man, thin-lipped, and with blue veins showing about his temples, thrust his head cautiously through the opening. The sweat was running from his moist and dirt-smeared face; a look of relief came over his features at the sight of the others. Durkin wondered just why he should be dressed in the peaked cap and blue suit of a Consolidated Gas Company inspector. The room into which they stepped had, obviously, once been a sewing-room. In one corner still stood the sewing-machine itself, in the shadow, incongruously enough, of a large safe with combination lock. Next to this stood a stout work-table, on which rested a box relay and a Bunnell sounder. Around the latter were clustered a galvanometer, a 1-2 duplex set, a condenser, and a Wheatstone bridge of the Post-Office pattern, while about the floor lay coils of copper wire, a pair of lineman’s pliers, and a number of scattered tools. Durkin’s trained eye saw that the condenser had been in use, to reduce the current from a tapped electric-light wire; while the next moment his glance fell on a complete wire-tapping outfit, snugly packed away in an innocent enough looking suit-case. Then he turned to the two men and the woman, as they bent anxiously over the littered table, where Mackenzie was once more struggling with his instrument, talking quickly and tensely as he tested and worked and listened. “Great Scott, Mack, it’s easy enough for you to talk, but it was fool’s luck, pure fool’s luck, I ever got this wire up! First, I had forty feet of water-pipe, then eighty feet o’ brick wall, then over fifty feet of cornice, and about twice as much eave-trough, hangin’ on all the time by my eyelashes, and dog-sick waitin’ to be pinched with the goods on! Hold on, there—what’s this?” The sounder had given out a tremulous little quaver; then a feeble click or two; then was silent once more. “Lost it again!” said Mackenzie, under his breath. “Let me look over that relay a minute!” broke in Durkin. It was the type of box-relay usually used by linemen, with a Morse key attached to the base-board; and he ran his eye over it quickly. Then, with a deft movement or two he released the binding of the armature lever screws, and the next moment the instrument felt the pulse of life, and spoke out clearly and distinctly. Mackenzie looked up at the newcomer, for the first time, with an actual and personal interest. “That’s the trick, all right!” he said, with an admiring shake of the head.