This book is a sequel to the book " The Secret of the Unicorn ". Previously, Tintin and Capt. Haddock had retrieved three scrolls, showing them a place to hunt for the treasure of the Captain's ancestor, Sir Francis Haddock.
The story opens, showing a pub. The Captain's ship's cook is talking to his friend about his pending journey to search for a treasure. But he hesitates, when he sees a man overhearing them.