Based on a novel by Mignon G. Eberhart, a private investigator in the hospital for a rest and a nurse help solve murder cases that occur there.
Insurance investigator Lance O'Leary (Patric Knowles) walks out asleep in pajamas. Inspector Foley (Cliff Clark) sprays O'Leary with a hose to wake him, and Dr. Arthur Lethany (Harland Tucker) takes him to a hospital. Nurse Sara Keate (Ann Sheridan) finds O'Leary in room 18 and, irritated by personal questions in the past, transfers him to 13. O'Leary gets up and kisses her. Dr. Balman (Charles Trowbridge) complains to Dr. Lethany that $100,000 of radium is being used for rich Frank Warren (Edward McWade) in room 18. Carol Lethany (Jean Benedict) meets Jim Warren (John Ridgely), who is engaged to nurse Maida Day (Rosella Towne). Dr. Lethany tries to embrace Maida, who resists and complains. Frank Warren refuses to give his nephew Jim Warren money.
During rain someone locks Sara in with O'Leary and turns off the lights. From a window drunk janitor Joe Higgins (Frank Orth) sees a man take radium from Frank Warren and hide it in a flower pot. Sara and Dr. Fred Hajek (Edward Raquello) turn on the lights, and they find Frank Warren is dead. Dr. Balman says that he died of a morphine overdose, and the radium is missing. Dr. Lethany has disappeared. Foley lets O'Leary help with the case and shows him a diamond clasp. Foley questions Dr. Hajek, who says he was with Carol Lethany. Foley finds O'Leary's man Bentley (Eric Stanley) looking in the closet in room 18, and Bentley used to work for Warren. O'Leary finds the body of Lethany in the closet. O'Leary calls on Carol Lethany and asks her about a pistol with her initials that he says killed Lethany.
O'Leary finds Higgins hung over, and Higgins says he saw Lethany murdered. O'Leary looks in the bushes as Higgins disappears. Sara gives Maida the flower pot. Higgins calls Sara, who tells him to come back. Someone grabs Higgins. Sara and Dr. Balman find Higgins stabbed in room 18. Maida shows Sara the radium in the pot, and Sara tells O'Leary and Foley. O'Leary tells Maida to put the flower pot back in room 18. Someone comes out of the closet and takes the radium. All meet, and O'Leary says that Lethany killed Warren, and Maida's clasp was found in his pocket. Dr. Lethany comes in and says that Dr. Balman knocked him out. O'Leary accuses Dr. Balman of killing Warren and Higgins. Dr. Balman grabs a gun but is shot. O'Leary gives Foley the credit and asks for a reward from Sara, who puts him to bed and kisses him.
This lively mystery moves quickly though the unexpected ending results from an improbable motive.