Fifteen-year-old John Trenchard lives in the coastal village of Moonfleet, where Colonel 'Blackbeard' Mohune's ghost is said to roam each night in search of his long-lost diamond. When John stumbles upon Blackbeard's coffin, he finds a mysterious clue to the whereabouts of the legendary jewel. Drawn into the secretive and dangerous world of smuggling, John soon finds himself on the run for his life...!