Billy and Sheena go with their Uncle, Dr. Deep, to search for treasure and are pursued by pirates who have been dead for two hundred years, and when Billy and Sheena return to land and visit Horrorland they encounter their worse fears.
Visiting their uncle's seaside home for the summer, a brother and sister open a mysterious trunk in a back room and discover a sinister-looking pirate puppet that comes to life and takes them captive.