Down-on-his-luck entrepreneur Bill Martin and sidekick Stuff Oliver try to stay one step in front of creditors in their seedy waterfront office when they meet "The Captain," an idiosyncratic peg-legged old sailor. The Captain is convinced that the treasure of pirate Sir Henry Morgan is hidden somewhere in a castle on an offshore island recently inherited by Martin. His proof is a treasure map, half of which has been stolen by a mysterious phantom who lurks in the shadows waiting for an opportunity to steal the other half. Sensing a moneymaking opportunity, Bill tries to recruit customers willing to pay $50 apiece for a "treasure hunt" outing to the "haunted" island. Among those signing up are heiress Wendy Creighton and her bored, ineffectual boy friend, a dimwitted police sergeant, a professor whose expertise is old maps, a wanted murderer and his moll, and Bill's cousin George, who has recently offered $20,000 to buy the supposedly worthless island. They all get more than the few goosebumps they bargained for as death and the phantom await them in the ghostly castle.