A hunch by Ellery Queen (George Nader) about a mysterious swimming death proves to have foundation. A former girlfriend pleads with Queen for $15,000, scribbles the name of a small Key West hotel on a napkin and vanishes. Queen catches up with her at the hotel only to find her happy, carefree, and no longer in need of money. But when a man she knows dies in a swimming accident, Ellery orders an autopsy and uncovers a murder