The Markenmore Mystery by J.S. Fletcher

The man whom Braxfield thus addressed, and who, in spite of the well-remembered signal on the pantry window was the last person in the world he had thought of seeing, turned a sharp, inquisitive, suspicious glance down the narrow passage, which opened on the main corridor of the house. It shifted just as sharply to the old butler's amazed and troubled face-and the question that followed on it was equally sharp.

"The rest of 'em-in bed?"