Now there are three children of the big three- Percy, Harold and Talia. Percy is confused about the prophecy. He can't understand who the prophecy talks about
Mr. Bruner, the owner of Camp Half Blood tells Percy there is a new quest which involves Cronus coming back to life.
Percy finds out that Cronus has Poseidon and Zeus and tells Harold, Talia, Annabeth and Grover and they leave immediately to find them and kill Cronus
They see Cronus eat Hades and find out that is where Poseidon and Zeus are. They wait till he sleeps , so they can kill him. Percy thinks if the prophecy talks about all three children of the big three.
Talia and Harold used their powers in such a way that they got Percy an easy stab to Cronus and get their fathers out of the stomach.
In the end, Percy realizes that the prophecy talks about all the children of the big three