A playwright descended from the Borgia family becomes a murder suspect.

In a spooky hotel on the coast of France, two bands of crooks are working independently of the other in an attempt to steal the inherited fortune of an American girl, Sue Tally. Along the way the heiress is kidnapped, three murders are committed, a girl appears in two places at once, mysterious persons roam about the old hotel at night and mysteriously disappear, and there is a hidden room without any doors.

Choreographer Bob Connolly and prolific screenwriter Crane Wilbur teamed up on the direction of Warner Bros.' The Patient in Room 18. Patric Knowles delivers a delightfully comic performance as Lance, an outwardly normal young man obsessed with detective stories. When his obsession threatens to lapse over into lunacy, Lance is sent to the hospital for a nice long rest. It isn't long before he gets mixed up in a genuine murder mystery, using his second-hand knowhow to solve the case. Up-and-coming Ann Sheridan is quite amusing as Lance's nurse and confidante, while the murderer is played by a fellow who is usually cast as the murder victim.

A wealthy family is blackmailed. Murder results. And a nurse at the scene of the crime is determined to figure out who-done-it.

When a businessman is found dead in a seclusion house, it is initially ruled as a suicide. However, a detective suspects foul play and begins to investigate, uncovering a web of deceit and murder. As the detective delves deeper, he discovers a love triangle, hidden clues, and a chain of events that make the case more complex than it first appears.

A murder happens when greedy relatives gather to await the demise of their wealthy and very ill family patriarch.