It Walks by Night

A ghastly crime... Monsieur de Saligny was found in a card-room of a gambling palace and secret opium den, knelt in supplication, the bloody stump where his head should have been bowed forward and resting on the floor. The head lay propped up facing toward the door several feet away. No one was seen entering or leaving the room between when M. de Saligny entered the room and when the body was discovered. Will shrewd detective Bencolin be able to solve the first whodunnit penned by the master of the locked room mystery, John Dickson Carr?