A Gentleman of Leisure by P. G. Wodehouse

How long the light had been darting about the room like a very-much-enlarged firefly Jimmy did not know. It seemed to him like hours, for it had woven itself into an incoherent waking dream of his; and for a moment, as the mists of sleep passed away from his brain, he fancied that he was dreaming still. Then sleep left him, and he realised that the light, which was now moving slowly across the bookcase, was a real light.

That the man behind it could not have been there long was plain, or he would have seen the chair and its occupant. He seemed to be taking the room step by step. As Jimmy sat up noiselessly, and gripped the arms of the chair in readiness for a spring, the light passed from the bookcase to the table. Another foot or so to the left, and it would have fallen on Jimmy.