In 1699, pirate Captain Kidd plunders and destroys the English galleon The Twelve Apostles near Madagascar, burying the stolen treasure on a remote island.
He returns to London and, seeking a fresh start, hires a gentleman's gentleman before presenting himself at the court of William III of England as an honest shipmaster intent on earning a royal commission as a privateer after striking his colours to a pirate. The king, convinced by Kidd’s tale that the captain of The Twelve Apostles was the pirate who disappeared with its treasure, grants the commission and raises Kidd to a status he hadn’t earned through reputation alone.
Kidd then recruits a crew from condemned pirates in Newgate and Marshalsea prisons, promising them a royal pardon at the voyage’s end. Among the recruits is the quarrelsome yet cultivated Adam Mercy, chosen as the new master gunner on the strength of claimed prior service with pirate Captain Avery. Kidd’s confidence deepens when he assigns Mercy to a role essential to the voyage’s plans, reinforcing the idea that mercy—political or personal—will come to those who deserve it in this dangerous game.
The king sends Kidd and his ship Adventure Galley toward the waters near Madagascar to rendezvous with the Quedagh Merchant and escort it back to England. The Quedagh Merchant carries Lord Fallsworth, the king’s ambassador to the Grand Mughal, his daughter Lady Anne Dunstan, and a chest of treasure destined for King William. Kidd’s beguiling account of a pirate fight nearby sways Fallsworth to swap ships with his daughter and the precious cargo, a move that will have repercussions long after it’s made.
The Quedagh Merchant is blown up in a catastrophic explosion, and Lady Anne finds herself turning for support to Kidd’s servant, Cary Shadwell, the one man she thinks she can trust. Shadwell tells her that the earlier battle never happened, and he urges her to place her faith in Adam Mercy again, steering her toward a different form of loyalty that Kidd did not anticipate.
On the voyage home, Kidd schemes to rid himself of his three closest accomplices (to keep the booty for himself) and of Mercy, whom he suspects of being a traitor. Mercy—who is really the vengeance-seeking son of Admiral Lord Blayne, the slain captain of The Twelve Apostles—becomes a focal point of Kidd’s paranoia. When a smitten Lorenzo tries to force himself on Lady Anne, Mercy steps in to defend her in a swordfight, a clash that ends with Lorenzo driven overboard and presumed dead. During the confrontation, Mercy’s medallion is torn from his neck, and Kidd finds it, recognizing the Blayne family crest and suspecting that Mercy is a relative of the murdered captain.
Kidd drops anchor at a lagoon with Orange Povey, his only surviving confederate, who is protected by an incriminating letter that would humiliate the crown if Povey should die. Povey is joined by Mercy and Kidd onshore to dig up the loot from The Twelve Apostles. When Mercy sees the Blayne crest, he pretends indifference, but Kidd goads him by insulting his dead father’s honor, pushing Mercy toward a breaking point. Mercy is enraged and attacks Kidd and Povey; outnumbered, he is knocked unconscious, falls into the water, and does not resurface. Believing him dead, the others think the danger has passed, but Mercy secretly swims back to the ship and survives.
Mercy and Bart Bart Blivens row Lady Anne away in the ship’s jolly boat, but they are spotted. Shadwell sacrifices himself to cover their escape, and Kidd blows up the jolly boat in a final bid to hold onto his prize.
Believing himself safe, Kidd appears before the king again with the Mughal treasure, hoping for the reward of a title and the estate of Lord Blayne. He soon learns that Mercy and Lady Anne have survived and outrun him to court, and that the crown’s men have already found the loot from The Twelve Apostles after a search of Kidd’s cabin. The web of deceit tightens as Kidd is finally apprehended, tried, condemned, and hanged for his crimes.
