The Fourth Door (Unabridged‪)‬

Jessica Standish is fatally stabbed with an oriental dagger in her own bedroom. Her murderer is seen escaping from the scene by her brother, who identifies him as her former fiancé, Arthur Caldon. Later that same night, Caldon's cottage burns to the ground, but he's not inside. Instead, he vanishes.

Inspector Betteridge, the chief investigator of the murder, learns that the dagger had definitely belonged to the missing man; but he also uncovers many puzzling strands to the affair. Arthur has an estranged twin brother, Drake Caldon, owner of the nearby Caldon Manor. The inspector's suspicions and inquiries encompass not only Drake, but also his new and beautiful wife, Elva, and his estate manager and cousin, Barry Wood. Then Elva disappears....