Gunman's Bluff by Edgar Wallace

During the hours which Luke Maddison had spent in his prison house, it was curious that he should think so little on serious topics. He was face to face with death in its most hideous aspect -- it was impossible to mistake Connor's intention -- and yet for the main part his mind was occupied by the veriest trivialities. If he thought of Margaret at all it was only in a detached and impersonal way and to find an explanation for her presence with the police at his flat that night. She must have had the key; the police went to her -- but why?

Then he remembered his conversation with Hulbert's servant, who had obviously been suspicious and must have communicated at once with the nearest police station.