Suddenly I saw a light shine for a second up in the direction of the ventilator, but it vanished immediately. Then was 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 everything was silent once more, though the smell grew stronger. For half an hour I sat with straining ears. Then suddenly I heard another sound. It was a very gentle, soothing sound, like that of a steam coming from a kettle. The instant that we heard it, Holmes jumped from the bed, struck a light, and hit furiously with his stick at the bell-pull.

"You see it, Watson?" he shouted. "You see it?"

But I saw nothing. At the moment when Holmes struck the light I heard a low, clear whistle, but the sudden light flashing into my tired eyes made it impossible for me to tell what it was that my friend was hitting so savagely. I could, however, see that his face was very pale and filled with horror and loathing. He he stopped hitting, and stared up at the ventilator. Then suddenly there came from the silence of the night the most horrible cry which I have ever heard.