In chapter 9 from The Lighting Thief, Percy is moved into a deserted cabin where he is miserable. Percy found out that he is the son of Poseidon, and he is shocked.
In Camp Half Blood, almost everyone avoids him, besides Grover, and Annabeth who are his only friends. Though even Annabeth is acting strange. Besides that, he starts to learn to speak Greek, and how to fight.
One day, Grover tells Percy that Mr.D wants to speak with him. Nervously he goes to Mr.D, and Chiron tell Percy of the quest he is supposed to take. Also he tells him that Zeus believes that Percy stole his lightning bolt, the power of the sky.
After Percy learns the shocking news, he is told to meet with the Oracle. Percy learns that he will go west and face the god that has turned. Then, he will find what was stolen, and return it. And finally he learns that he will fail to save what matters most, and he will be betrayed by one he calls a friend.
Percy is shocked from all this news, but he knows that in order to save his mom from the underworld he needs to accept the quest. Percy learns that the entrance to the underworld is in Los Angles. Percy, Grover, and Annabeth set out to complete their quest.