The film's prologue was 8 years before the action of the main film - with the British vessel the HMS Dauntless encountering evidence of a pirate ship's (the Black Pearl with black sails) attack on a merchant vessel. Future characters were introduced: 12 year-old Elizabeth Swann, daughter of Port Royal's (Jamaica) Governor Weatherby Swann (Jonathan Pryce), a rescued boy named Will Turner (with a mysterious gold pirate's medallion with a skull, secretly kept by Elizabeth), and ship's lieutenant James Norrington (Jack Davenport).
In the film's main story, Captain Norrington was being promoted to Commodore in the British Royal Navy, and Will Turner (Orlando Bloom) was Port Royal blacksmith's apprentice and expert swordsman, in love with spunky 20 year-old Elizabeth Swann (Keira Knightley). Swashbuckling, eccentric pirate Captain Jack Sparrow (Johnny Depp) arrived in Port Royal, Jamaica, just as his dinghy sank at the dock in the film's clever entrance scene.
He arrived just in time to save Elizabeth (with the medallion around her neck, emitting a pulse in the water) who had fainted and fallen into the ocean after the promotion ceremony. Sparrow was captured and locked up in jail, ready to be hanged by Elizabeth's pompous fiancee Commodore Norrington the next day.
Meanwhile, blackhearted Captain Hector Barbossa (Geoffrey Rush) and his crew of "miscreants"-pirates from the Black Pearl (Jack's former boat), attacked Port Royal, summoned by Elizabeth's medallion, and kidnapped her. She was mistaken for the daughter of pirate-scallywag William "Bootstrap Bill" Turner, Will's father, when she told Barbossa her name was Elizabeth Turner, and they kept her onboard when she turned over the medallion, and kept her captive on their trip to Isla de Muerta.
Will Turner freed Jack from jail to help him rescue his "bonny lass" Elizabeth from the Black Pearl, by commandeering the HMS Interceptor (after tricking the Navy by switching ships). They sailed on to Tortuga to first assemble a motley buccaneer crew before proceeding after Elizabeth.
Meanwhile, Barbossa explained to Elizabeth how the medallion was "Aztec gold, one of 882 identical pieces they delivered in a stone chest to Cortes himself. Blood money paid to stem the slaughter he wreaked upon them with his armies. But the greed of Cortes was insatiable. So the heathen gods placed upon the gold a terrible curse. Any mortal that removes but a single piece from that stone chest shall be punished for eternity" - after Barbossa located the chest and stole the Aztec gold coins (and wastefully spent all of them), the ancient curse was placed on him and his greedy crew ("We are cursed men") - they were doomed to sail the seas as living corpses.
While sailing to Isla de Muerta, Will learned that ten years earlier, Captain Jack was formerly the captain of the Black Pearl when Barbossa was the First Mate - who had mutinied, marooned Jack on an isolated island to die (although he escaped three days later by making a raft of sea turtles - one of his tall tales), and stolen the cursed treasure of Cortes' Aztec gold coins. Barbossa arrived at Isla de Muerta where the treasure was stored in a stone chest, to lift the curse by performing "the blood sacrifice owed to the heathen gods" on the medallion with Elizabeth's blood - chanting: "Begun by blood. By blood undone"; but the blood from a knife cut on her hand that was spilled on the medallion had no effect!
Will knocked out Jack and rescued Elizabeth (she grabbed the medallion) in the confusion and brought her to the Interceptor while Jack was captured by Barbossa's pirates - and then he bargained with his life, trading his knowledge of whose blood they needed. [The medallion was a gift from Will's father to him, and Will's blood ("the blood of a pirate") was what the pirates really needed.]. After the Black Pearl came upon the Interceptor and sank it, a deal was made: Will was to be taken to Isla de Muerta for the ritual in exchange for Barbossa freeing Elizabeth, although in the end, she was marooned with Jack on an island after they both walked the plank.
A signal fire from a cache of rum alerted Commodore Norrington to the island - he then assisted in the rescue of Will (in exchange for Elizabeth's promise to marry him - "as a wedding gift") with the help of the Royal Navy and the HMS Dauntless. By film's end - after the pirates had surprise-attacked the Dauntless and conniving Captain Jack (who became temporarily 'undead' when he stole a coin) had a long swordfight with Barbossa which ended when he shot him in the heart, Elizabeth helped rightful heir Will to defeat the pirates and return the final two bloodied coins to the treasure chest to finally break the curse (and kill the fatally-wounded, now-mortal Barbossa).
Will rescued pirate Jack from hanging by the Navy in Port Royal, and he escaped with his freed crew on the Pearl ("with one day's head start"), while Elizabeth's profession of her heart's true love for a pardoned Will was accepted by Norrington.
