Tintin, Snowy and Captain Haddock set off to find the long-lost treasure of Red Rackham the pirate. From their discoveries in the Le secret de La Licorne they possess the vital clue to the treasure's hiding-place. But this is no easy search, particularly when the detectives Thomson and Thompson, and Professor Calculus, are in the party. After strange finds on a desert island, and hazardous underwater adventures, the treasure-hunt has an unexpected ending.