The Patient in Room 18 (1938)

Unable to solve his last case, famed private detective Lance O'Leary is showing signs of being on the verge of a nervous breakdown, so he is admitted to the private Thatcher Institute to recuperate. Beyond his inability to rest and relax as ordered, O'Leary doesn't totally mind being there; it lets him spend time with head nurse Sara Keate, with whom he is in an on/off relationship, the switches pressed by her. Besides O'Leary's butler Seymour Bentley being a known ex-con, much of intrigue is happening at the Institute: the only other patient is elderly, wealthy Institute benefactor Frank Warren, whom head doctor Arthur Lethany convinced to go through a $100,000 medical radium treatment for his ailment; Dr. Balman, who once had money but is now broke, is incensed by the treatment as he feels it is both unnecessary for Warren and would better serve a multitude of other patients who would truly benefit from it; Lethany's wife Carol is in a clandestine relationship with the Institute's poor intern, Dr. Fred Harker, for whom she would leave her husband if Harker only had money; Lethany himself lusts after another of the nurses, Maida Day; Warren's nephew Jim Warren is deeply in debt and his uncle refuses to help him pay; and Jim and Maida themselves are in a relationship. Within these situations, two of these people are murdered at the Institute and the $100,000 worth of radium stolen, all the other players who would have opportunity and/or motive to kill one or both victims. Thus, O'Leary changes from being patient back to private investigator, and Sara is by his side in the investigation despite being a suspect herself. Things are only complicated as O'Leary and the police detective in charge of the case, Inspector Foley, have a friendly rivalry. The case takes a turn when some discover that the Institute's nightwatchman, Higgins, actually saw the murder.