Elusive Isabel  (English, Paperback, Futrelle Jacques)

He walked around the room once, opening and shutting the doors of the cabinets as he passed, and finally paused in front of the safe. A brief examination of the nickeled dial and handle and of the enameled edges of the heavy door satisfied him that no force had been employed--the safe had merely been unlocked. Whereupon he sat himself down, cross-legged on the floor, in front of it.