"My God!" I whispered; "did you see it?"

Holmes was for the moment as startled as I. His hand closed like a vice upon my wrist in his agitation. Then he broke into a low laugh and put his lips to my ear.

"It is a nice household," he murmured. "That is the baboon."

I had forgotten the strange pets which the doctor affected. There was a cheetah, too; perhaps we might find it upon our shoulders at any moment. I confess that I felt easier in my mind when, after following Holmes' example and slipping off my shoes, I found myself inside the bedroom. My companion noiselessly closed the shutters, moved the lamp onto the table, and cast his eyes round the room. All was as we had seen it in the daytime. Then creeping up to me and making a trumpet of his hand, he whispered into my ear again so gently that it was all that I could do to distinguish the words:

"The least sound would be fatal to our plans."

I nodded to show that I had heard.

"We must sit without light. He would see it through the ventilator."

I nodded again.

"Do not go asleep; your very life may depend upon it. Have your pistol ready in case we should need it. I will sit on the side of the bed, and you in that chair."

I took out my revolver and laid it on the corner of the table.

Holmes had brought up a long thin cane, and this he placed upon the bed beside him. By it he laid the box of matches and the stump of a candle. Then he turned down the lamp, and we were left in darkness.

How shall I ever forget that dreadful vigil? I could not hear a sound, not even the drawing of a breath, and yet I knew that my companion sat open-eyed, within a few feet of me, in the same state of nervous tension in which I was myself. The shutters cut off the least ray of light, and we waited in absolute darkness.

From outside came the occasional cry of a night-bird, and once at our very window a long drawn catlike whine, which told us that the cheetah was indeed at liberty. Far away we could hear the deep tones of the parish clock, which boomed out every quarter of an hour. How long they seemed, those quarters! Twelve struck, and one and two and three, and still we sat waiting silently for whatever might befall.

Suddenly there was the momentary gleam of a light up in the direction of the ventilator, which vanished immediately, but was succeeded by a strong smell of burning oil and heated metal. Someone in the next room had lit a dark-lantern. I heard a gentle sound of movement, and then all was silent once more, though the smell grew stronger. For half an hour I sat with straining ears. Then suddenly another sound became audible–a very gentle, soothing sound, like that of a small jet of steam escaping continually from a kettle. The instant that we heard it, Holmes sprang from the bed, struck a match, and lashed furiously with his cane at the bell-pull.