It was half-past six by that time, and growing dusk.

“You boy, down there!” I called.

The paper boy turned and looked around.  Then, seeing nobody, he raised his eyes.  It was a moment before he located me:  when he did, he stood for one moment as if paralyzed, then he gave a horrible yell, and dropping his papers, bolted across the lawn to the road without stopping to look around.  Once he fell, and his impetus was so great that he turned an involuntary somersault.  He was up and off again without any perceptible pause, and he leaped the hedge—­which I am sure under ordinary stress would have been a feat for a man.

I am glad in this way to settle the Gray Lady story, which is still a choice morsel in Casanova.  I believe the moral deduced by the village was that it is always unlucky to throw a stone at a black cat.

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.