“How long had Inspector Whiteleaf and this dark horse in the fur coat been gone at the time you heard the noise?”

“About half an hour, sir.”

“Do you think the noise came from the landing or from one of the offices above?”

“An office I should say.  It was very dim.”

Chief Inspector Kerry pushed upon the broken door, and walked into the rooms of Kazmah.  Flashing the ray of his torch on the wall, he found the switch and snapped up the lights.  He removed his overall and tossed it on a divan with his cane.  Then, tilting his bowler further forward, he thrust his hands into his reefer pockets, and stood staring toward the door, beyond which lay the room of the murder, in darkness.

“Who is he?” he muttered.  “What’s it mean?”

Taking up the torch, he walked through and turned on the lights in the inner rooms.  For a long time he stood staring at the little square window low down behind the ebony chair, striving to imagine uses for it as his wife had urged him to do.  The globular green lamp in the second apartment was worked by three switches situated in the inside room, and he had discovered that in this way the visitor who came to consult Kazmah was treated to the illusion of a gradually falling darkness.  Then, the door in the first partition being opened, whoever sat in the ebony chair would become visible by the gradual uncovering of a light situated above the chair.  On this light being covered again the figure would apparently fade away.

It was ingenious, and, so far, quite clear.  But two things badly puzzled the inquirer; the little window down behind the chair, and the fact that all the arrangements for raising and lowering the lights were situated not in the narrow chamber in which Kazmah’s chair stood, and in which Sir Lucien had been found, but in the room behind it—­the room with which the little window communicated.

The table upon which the telephone rested was set immediately under this mysterious window, the window was provided with a green blind, and the switchboard controlling the complicated lighting scheme was also within reach of anyone seated at the table.

Kerry rolled mint gum from side to side of his mouth, and absently tried the handle of the door opening out from this interior room—­ evidently the office of the establishment—­into the corridor.  He knew it to be locked.  Turning, he walked through the suite and out on to the landing, passing the constable and going upstairs to the top floor, torch in hand.

From the main landing he walked along the narrow corridor until he stood at the head of the back stairs.  The door nearest to him bore the name:  “Cubanis Cigarette Company.”  He tried the handle.  The door was locked, as he had anticipated.  Kneeling down, he peered into the keyhole, holding the electric torch close beside his face and chewing industriously.

Ere long he stood up, descended again, but by the back stair, and stood staring reflectively at the door communicating with Kazmah’s inner room.  Then walking along the corridor to where the man stood on, the landing, he went in again to the mysterious apartments, but only to get his cane and his overall and to turn out the lights.