Billy and Sheena always expect adventure when they join their uncle, Dr Deep, abroad his high-tech boat. What they don't expect is a treasure hunt leading to a two-hundred-year-old sea captain... who refuses to stay dead! 

Just when they think the tide is turning, Billy and Sheena accidentally dive into a dangerous mystery. A chilling surprise awaits them in HorrorLand, the theme park where their worst nightmare is about to come to life.