Follaein on frae The Saicret o the Unicorn, Tintin an his freens mak for the Caribbean in search o the lang-tint treisure o pirate Rachlan the Reid. Aneth the waves they find the wrack o the ship, the Unicorn, but naither sign nor sicht o the treisure. They bring back nocht but an auld sea-kist fu of drookit documents — documents that are suin tae mak a bumbazin revelation!

Continuing from The Saicret o the Unicorn, Tintin and his friends head for the Caribbean in search of pirate Rachlan the Reid’s lost treasure. Beneath the waves they find the wreck of his ship, the Unicorn, but the treasure in nowhere to be found. They retrieve nothing but an old sea-chest full of sodden documents — documents which are set to divulge an astonishing revelation!