The full plot of On Stranger Tides follows one ritual: two silver chalices from Ponce de León's ship, the Santiago, plus a mermaid's tear. Blackbeard wants the Fountain because of a prophecy that he will die at the hands of a man with one leg, and he is willing to drag Jack, Angelica and a whole crew across the seas to beat death.
Blackbeard's crew captures a mermaid named Syrena, and a young missionary named Philip falls for her. Her tear is taken by force and she is left close to death. Barbossa, who has lost his leg to Blackbeard, wants revenge, and he stabs Blackbeard with a poisoned sword. That sets up the final stretch, with every faction converging on the Fountain at once.
At the Fountain, the Spanish arrive, toss the chalices into a pool and order the place destroyed. Philip frees Syrena, and she passes the chalices to Jack. Jack then tricks Blackbeard into drinking from the chalice that has no tear, and that is what kills him. Angelica is healed, Syrena forgives Philip, and the two return to the sea.
The aftermath splits the survivors. Barbossa takes over Blackbeard's ship, crew and sword, while Jack leaves Angelica stranded on an island. Gibbs uses Jack's compass to find the Revenge, and Jack recovers the Black Pearl from its bottle.