Percy receives the Great Prophecy from the Oracle: A Half-Blood of the eldest gods, Shall reach sixteen against all odds And see the world in endless sleep The hero's soul, cursed blade shall reap A single choice shall end his days Olympus to preserve or raze
The first event of the prophecy comes true when the entire town is put under endless sleep
Percy meets with Hades at the River Styx to gain the curse of Achilles; he does this so he can fight Kronos
Percy is tempted by Pandora's Box to set Hope free and surrender to Kronos because the prophecy makes it look like he is going to die by a cursed blade.
Percy learns that he is not the hero the prophecy speaks of. The blade that is spoken of is the knife Luke gave to Annabeth, along with a promise: he will never fail to protect them. The hero that will die is Luke, who is also the person who Kronos took possession of
Luke stabs himself in the weak spot with Annabeth's knife to kill Kronos and save Olympus, completing the Great Prophecy