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.