By means of a short ladder which Coombes had brought for the purpose Kerry climbed on to the wall and dropped into the yard.

“The jemmy!” he said softly.

Coombes, also mounting, dropped the required implement.  Kerry caught it deftly, and in a very few minutes had wrenched away the rough planking nailed over one of the lower windows, without making very much noise.

“Shall I come down?” inquired Coombes in muffled tones from the top of the wall.

“No,” rapped Kerry.  “Hide the ladder again.  If I want help I’ll whistle.  Catch!”

He tossed the jemmy up to Coombes, and Coombes succeeded in catching it.  Then Kerry raised the glass-less sash of the window and stepped into a little room, which he surveyed by the light of his electric torch.  It was filthy and littered with rubbish, but showed no sign of having been occupied for a long time.  The ceiling was nearly black, and so were the walls.  He went out into a narrow passage similar to that in the house of Sin Sin Wa and leading to a stair.

Walking quietly, he began to ascend.  Mollie Gretna’s description of the opium-house had been most detailed and lurid, and he was prepared for some extravagant scene.

He found three bare, dirty rooms, having all the windows boarded up.

“Hell!” he said succinctly.

Resting his torch upon a dust-coated ledge of the room, which presumably was situated in the front of the house, he deposited a cud of chewing-gum in the empty grate and lovingly selected a fresh piece from the packet which he always carried.  Once more chewing he returned to the narrow passage, which he knew must be that in which the secret doorway had opened.

It was uncarpeted and dirty, and the walls were covered with faded filthy paper, the original color and design of which were quite lost.  There was not the slightest evidence that a door had ever existed in any part of the wall.  Following a detailed examination Kerry returned his magnifying glass to the washleather bag and the bag to his waistcoat pocket.

“H’m,” he said, thinking aloud, “Sin Sin Wa may have only one eye, but it’s a good eye.”

He raised his glance to the blackened ceiling of the passage, and saw that the trap giving access to the roof was situated immediately above him.  He directed the ray of the torch upon it.  In the next moment he had snapped off the light and was creeping silently towards the door of the front room.

The trap had moved slightly!

Gaining the doorway, Kerry stood just inside the room and waited.  He became conscious of a kind of joyous excitement, which claimed him at such moments; an eagerness and a lust of action.  But he stood perfectly still, listening and waiting.

There came a faint creaking sound, and a new damp chilliness was added to the stale atmosphere of the passage.  Someone had quietly raised the trap.

Cutting through the blackness like a scimitar shone a ray of light from above, widening as it descended and ending in a white patch on the floor.  It was moved to and fro.  Then it disappeared.  Another vague creaking sound followed—­that caused by a man’s weight being imposed upon a wooden framework.