Dick Denver, a fifteen year old lad has just learnt from a friend that his father, a sailor, has died. Dick cannot bring himself to open the letter that accompanies this news – then there is a knock on the door and an unsavoury character, another mariner, barges in, insisting on seizing the letter. Dick escapes downstairs and bumps into Biggles, Algy and Ginger, who decide to help eject the intruder and retrieve Dick’s letter – which contains a gold doubloon and the location of where more could be found. Biggles and Co. do not hesitate to go on a treasure hunt to the Caribbean, but none of them know that the doubloon carries an ancient curse.