Pirates of the Caribbean Dead Man\'s Chest sub pl

William and Elizabeth are sentenced to death for being in contact with Jack Sparrow. For saving Elizabeth, Will accepts to bring Jack's compass in exchange for his and Elizabeth's freedom. Meanwhile, Jack is being hunted by Davy Jones. Elizabeth escapes from prison to look for Will. Jack agrees to trade Will his compass if he finds a special key that will open a special chest. To find the key, Will goes aboard the Flying Dutchman, upon which he gets captured. He is reunited by his father on the Flying Dutchman. He finds the key and escapes the ship. Meanwhile, Jack gets Elizabeth to find the chest containing the heart of Davy Jones. Will and Elizabeth reunite on the island and open the chest and find the heart of Davy Jones. While Jack wants it to settle his debt to Jones, Will wants it to free his father and another person wants it for his own needs. Who is this mysterious person and what does he want to do with it?