“Good Heavens, man,” I said irritably. “Don’t you ever go home and go to bed?” He closed the vestibule door behind him and cavalierly turned out the light. Our dialogue was sharp, staccato. “Have you a key to the empty house next door?” he demanded. “Somebody’s in there, and the latch is caught.” “The houses are alike. The key to this door may fit. Did you see them go in?” “No. There’s a light moving up from room to room. I saw something like it last night, and I have been watching. The patrolman reported queer doings there a week or so ago.” “A light!” I exclaimed. “Do you mean that you—” “Very likely,” he said grimly. “Have you a revolver?” “All kinds in the gun rack,” I replied, and going into the den, I came back with a Smith and Wesson. “I’m not much use,” I explained, “with this arm, but I’ll do what I can. There may be somebody there. The servants here have been uneasy.” Johnson planned the campaign. He suggested on account of my familiarity with the roof, that I go there and cut off escape in that direction. “I have Robison out there now—the patrolman on the beat,” he said. “He’ll watch below and you above, while I search the house. Be as quiet as possible.” I was rather amused. I put on some clothes and felt my way carefully up the stairs, the revolver swinging free in my pocket, my hand on the rail. At the foot of the ladder I stopped and looked up. Above me there was a gray rectangle of sky dotted with stars. It occurred to me that with my one serviceable hand holding the ladder, I was hardly in a position to defend myself, that I was about to hoist a body that I am rather careful of into a danger I couldn’t see and wasn’t particularly keen about anyhow. I don’t mind saying that the seconds it took me to scramble up the ladder were among the most unpleasant that I recall. I got to the top, however, without incident. I could see fairly well after the darkness of the house beneath, but there was nothing suspicious in sight. The roofs, separated by two feet of brick wall, stretched around me, unbroken save by an occasional chimney. I went very softly over to the other trap, the one belonging to the suspected house. It was closed, but I imagined I could hear Johnson’s footsteps ascending heavily. Then even that was gone. A near-by clock struck three as I stood waiting. I examined my revolver then, for the first time, and found it was empty!