After their play about Inspector Desmond of Scotland Yard folds, actors Keith Neville and Dan “Scooter” Casey try to return to New York. Their limited funds take them to Keysport, where bus companion Julie Graham advises them to see Annie Botts, owner of the Hotel Bellview, about a room. The pair secure two rooms and settle in for the night. Keith hears a woman yelling at a man in the room adjoining his, then hears a gunshot. He tells Casey to summon the police, then goes into the adjoining room to investigate. The killer slips into Keith’s room and escapes after locking Keith in with the dead man, wealthy businessman John Platt. When the police arrive, they suspect Keith and Casey of the murder, until Annie reveals that Platt came to the hotel with his secretary, Charlie Graham, who is Julie’s father. Charlie is questioned, and when the police find him carrying $5,000, which he maintains Platt gave to him for his faithful service, he is arrested. While Julie is calling Platt’s attorney, Clarence Fredericks, the police find Keith’s prop scroll announcing him as Inspector Desmond and requesting police cooperation. The scroll is taken to police chief T. J. McDougal and District Attorney Al Ross, who, taking the scroll for a real document, release Keith and Casey and hold a press conference announcing their assistance. The next day, Platt’s widow Alma hires the actors to recover the $5,000 that her husband was carrying when he died. Keith is reluctant to take the case but agrees to help when Julie asks him to clear her father. Keith decides that the killer might be revealed if they have Julie, dressed in a long coat and black veil, pose as the mystery woman and lurk about the murder room. The plan backfires, however, when the killer, who is searching the room for the missing money, knocks out Julie, steals her costume and escapes. The police find Julie’s purse after sighting the mysterious figure and deduce that she is the killer. While the hunt for Julie begins, Alma’s brother, Jack Webster, calls three people and arranges to meet them at a deserted cabin. Keith goes to the cabin after Jack promises evidence about the murderer, but falls asleep when nothing happens. The police, summoned by Fredericks after Julie calls him, go to the cabin later that night and find Jack dead. Julie is suspected of the latest murder, while Ross discovers that Keith is an actor. Ross cannot reveal the mix-up because of his own involvement, and so orders Keith and Casey to leave town. They return to the hotel, where Keith receives a message to go to Alma’s house. While Keith is at Alma’s, Casey and Annie find the missing money hidden in the bed in Platt’s room, and Julie goes to find Keith. Alma is about to reveal the killer’s identity to Keith, when she is shot and wounded, after which Keith runs into Julie’s car as he chases the gunman. He tells her to go to Fredericks while he returns to Alma, who is now being tended to by Ross. Ross then orders Keith to follow Julie, and he goes to Fredericks’ house, arriving in time to protect Julie from Fredericks, whom Julie has discovered is the killer. The police arrive, and Fredericks reveals that he killed Platt, who was blackmailing Alma, out of love for her. He killed Jack for trying to blackmail him, and then shot Alma in panic when she was about to reveal his name. The crime’s solution creates enough publicity to reopen Keith and Casey’s play, and they return to New York with Keith’s new wife Julie, and Annie, who is in love with Casey. More on Wikipedia or Mubi
Watch The Mysterious Miss X (1939)
