Detective Lance O'Leary, who is suffering from a nervous disorder caused by his failure to solve his last case, is sent to the hospital to recover. Sarah Keate, Lance's girl friend, is a nurse at the hospital. Lance's neighbor in room 18 is wealthy Frank Warren, whose son Jim is in love with nurse Maida Day. Dr. Arthur Lethany, Warren's doctor, has ordered an expensive dose of radium to cure Warren's skin disorder, to the dismay of his colleague, Dr. Bolman, who would rather see the radium used to cure poor people. Bolman resents Warren because his father was ruined by a stockbroker like Warren. Warren has also alienated his son by forbidding him to see Maida and refusing him needed money. Lethany's wife Carol is in love with intern Dr. Hajek and promises to leave her husband if Hajek can find enough money to support her. Lethany himself is in love with Maida, who turns him down for Jim. That night, after a dinner party at the Lethanys', Warren is murdered and the radium stolen. At the same time, Lethany disappears. When Warren's death, which was caused by an overdose of morphine, is discovered, Lance investigates, determined to solve this case. Shortly afterward, Lethany's body is found in the closet of Warren's room. Then Higgins, the hospital janitor, tells Lance that he witnessed the murder, but before he can name the murderer, he is murdered himself. Meanwhile, Maida discovers the radium hidden in the bottom of a plant. Lance instructs her to return the plant to room 18 and then hides in a closet, hoping to discover the murderer. When that plan fails, he gathers all the suspects in the solarium, including Lethany, who is not actually dead. Lethany confesses to stealing the radium and identifies Bolman as his assailant and Warren's murderer.