Yes, in "The Son of Neptune," which takes place 9 months after the last Olympian, Percy loses his memories. He must reach Camp Jupiter and flee the creatures that are attempting to murder him. During this time, he learns that he is the son of Poseidon, the God of the Sea; and that he has been sent to save Greece from the monster Scylla. Poseidon was angry with Zeus because Olympus had been taken over by humans. So, to punish them, he made them look like fools by making them believe that they had lost their son. To escape this punishment, they decided to send him on a dangerous mission. Since humans cannot go under water, Poseidon gave them Hermes as a companion who could travel underwater. With him, they would be able to find Scylla. However, since humans are weak, they needed something to help them fight off the monsters. So, they gave Percy some special powers that no human has ever had before. With these powers, he was able to defeat the monsters and save Greece from destruction. After this incident, Percy's parents realized that they had been wrong about not trusting humans enough. They told him to go back home but he refused because he wanted to know more about other worlds. So, they sent Hermes back to help him.