 In the first of two films, followed by "Mystery House", in which Ann Sheridan played Mignon Eberhardt s Nurse Sarah Keate character (played previously at Warner s by Aline MacMahon and by Jane Darwell at 20th Century-Fox), private detective Lance O Leary (Patric Knowles), her off-and-on boyfriend, is recuperating from a nervous breakdown in Room 18 of the Thatcher Hospital. Wealthy patient Frank Warren (Edward McWade) is murdered in a nearby room, and a valuable supply of radium, used in his treatment, is stolen. Lane suspects Warren s son, Jim Warren (John Ridgely), when he discovers the father had turned him down on a loan for his failed business. And Jim s nurse sweetheart, Maida Day (Rosella Towne), is also suspected by Lance. While Police Inspector s Foley (Cliff Clark) and Donahue (Ralph Sanford) are investigating the Warren murder, they discover Dr. Arthur Lethany (Harland Tucker) murdered, and his body concealed in the closet in Warren s room. Lane thinks the missing radium holds the answer to both killings and, after Madia finds it and gives it to Lance, he places it where he knows the guilty person will attempt to steal it again. His plan is to make sure the killer is successful in the attempt.