The Fourth Door

When Jessica Standish is fatally stabbed with an oriental dagger in her bedroom, her brother sees the murderer's escape from the scene and identifies him as her former fiance Arthur Caldon. That same night, Caldon's cottage is burned to the ground, but he's not inside - he has vanished. Inspector Butteridge, investigating, finds that the dagger was Caldon's, and that he has a twin brother, Drake Caldon, who is newly married to the beautiful Elva. And then Elva disappears...