The Phantom from 10,000 Leagues

When a postmortem finds that a murdered fisherman was exposed to unusual amounts of radiation, Dr. Ted Stevens (Kent Taylor) decides to investigate. Out looking for clues, he meets a young beauty named Lois (Cathy Downs), whose father, Professor King (Michael Whalen), runs a local marine biology lab. Ted discovers that the elder King's secret experiments with atomic energy have resulted in the creation of a murderous aquatic beast, and he must act fast to prevent more needless deaths.