Tarling noted the door--noted, too the electric switch just in view.

Then the door opened slowly.

He saw Mrs.Rider's face light up with pleasure, then somebody asked a question in a whisper, and she answered--he could just hear her words: "No darling, nobody." Tarling held his breath and waited.

Then, of a sudden, the light in the room was extinguished.

Whoever had entered had turned out the light.
He heard a soft footfall coming towards the window looking into the conservatory and the rattle of the blinds as they were lowered.