With Johnny Sweeny a cloud of dust down the road, and the dinner-hour approaching, I hurried on with my investigations. Luckily, the roof was flat, and I was able to go over every inch of it. But the result was disappointing; no trap-door revealed itself, no glass window; nothing but a couple of pipes two inches across, and standing perhaps eighteen inches high and three feet apart, with a cap to prevent rain from entering and raised to permit the passage of air. I picked up a pebble from the roof and dropped it down, listening with my ear at one of the pipes. I could hear it strike on something with a sharp, metallic sound, but it was impossible for me to tell how far it had gone. I gave up finally and went down the ladder again, getting in through the ball-room window without being observed. I went back at once to the trunk-room, and, sitting down on a box, I gave my mind, as consistently as I could, to the problem before me. If the pipes in the roof were ventilators to the secret room, and there was no trap-door above, the entrance was probably in one of the two rooms between which it lay—unless, indeed, the room had been built, and the opening then closed with a brick and mortar wall. The mantel fascinated me. Made of wood and carved, the more I looked the more I wondered that I had not noticed before the absurdity of such a mantel in such a place. It was covered with scrolls and panels, and finally, by the merest accident, I pushed one of the panels to the side. It moved easily, revealing a small brass knob. It is not necessary to detail the fluctuations of hope and despair, and not a little fear of what lay beyond, with which I twisted and turned the knob. It moved, but nothing seemed to happen, and then I discovered the trouble. I pushed the knob vigorously to one side, and the whole mantel swung loose from the wall almost a foot, revealing a cavernous space beyond. I took a long breath, closed the door from the trunk-room into the hall—thank Heaven, I did not lock it—and pulling the mantel-door wide open, I stepped into the chimney-room. I had time to get a hazy view of a small portable safe, a common wooden table and a chair—then the mantel door swung to, and clicked behind me. I stood quite still for a moment, in the darkness, unable to comprehend what had happened. Then I turned and beat furiously at the door with my fists. It was closed and locked again, and my fingers in the darkness slid over a smooth wooden surface without a sign of a knob. I was furiously angry—at myself, at the mantel door, at everything. I did not fear suffocation; before the thought had come to me I had already seen a gleam of light from the two small ventilating pipes in the roof. They supplied air, but nothing else. The room itself was shrouded in blackness.