The Winding Stair by A.E.W. Mason

Si El Hadj Arrifa was right. When Mohammed saw Paul Ravenel ride forward out of the loom of the night into the darkness of the tunnel, bending his head so that it might not strike the roof, he missed a slight action which was much more significant. Paul slipped his right hand into his pocket and took out a heavy key. He had been seeing to it that Mohammed should draw gradually ahead and by the time when he came opposite to the little door in the angle, Mohammed was far beyond the turn and there was not the faintest glimmer of light from the lantern. Paul slipped from his saddle, gave his horse a sharp cut across the buttocks with his riding whip, and as the startled animal galloped off, turned quickly to the little door.

He was in a darkness so complete that he could not see the key in his hand nor the hand that held it. Yet he found the keyhole at once and in another second he was within the house. The passage in which he found himself was as black as the tunnel outside. Yet he locked the door, picked up and fitted the stout transverse bars into their sockets as neatly as though he worked in the broad noon. He had made no sound at all. Yet he had shut a door between the world and himself, and the effort of his life now must be to keep it for ever closed. He had a queer fancy that a door thus momentously closing upon his fortunes ought to clang so loudly that the noise of it would reach across the city.