“What is that?” asked Holmes, suddenly.
We all stood still and listened. A low moaning sound was coming from somewhere over our heads. Holmes rushed to the door and out into the hall. The dismal noise came from upstairs. He dashed up, the inspector and I at his heels, while his brother Mycroft followed as quickly as his great bulk would permit.
Three doors faced up upon the second floor, and it was from the central of these that the sinister sounds were issuing, sinking sometimes into a dull mumble and rising again into a shrill whine. It was locked, but the key had been left on the outside. Holmes flung open the door and rushed in, but he was out again in an instant, with his hand to his throat.
“It’s charcoal,” he cried. “Give it time. It will clear.”
Peering in, we could see that the only light in the room came from a dull blue flame which flickered from a small brass tripod in the centre. It threw a livid, unnatural circle upon the floor, while in the shadows beyond we saw the vague loom of two figures which crouched against the wall. From the open door there reeked a horrible poisonous exhalation which set us gasping and coughing. Holmes rushed to the top of the stairs to draw in the fresh air, and then, dashing into the room, he threw up the window and hurled the brazen tripod out into the garden.
“We can enter in a minute,” he gasped, darting out again. “Where is a candle? I doubt if we could strike a match in that atmosphere. Hold the light at the door and we shall get them out, Mycroft, now!”
With a rush we got to the poisoned men and dragged them out into the well-lit hall. Both of them were blue-lipped and insensible, with swollen,