Hector Lynch, wanted by the authorities in London for piracy, has come to St Mary's Island, near Madagascar, on his search for the elusive Libertalia - a settlement where it is said that all are allowed to live freely.
Here, he meets Captain Henry Avery, captain of the freebooter Fancy, which is sailing north through the Indian Ocean in search of a huge haul of gold. Avery requires a navigator, and persuades Hector and his friends Jacques and Jezreel to join the voyage, with the promise that they should be free to leave if they come across the fabled Libertalia on their travels.
Although Hector is reluctant to return once more to a life of piracy, his desperation to find a place he can finally settle with his wife Maria draws him in. The Fancy joins forces with other notorious pirate ships, including Thomas Tew's Amity, and as they sail up through the Arabian Sea, they encounter a convoy of the Grand Mogul's ships, including the Ganj-i-Sawa'i, the 'Exceeding Treasure', laden with riches. Soon, Hector finds himself caught up in one of the most deadly plunders in history . . .
