Percy's math teacher attempts to kill him, but fails. He is then sent to Camp Half-Blood, a camp for demigods like Percy. He is revealed as the son of Poseidon.
RETURN MY PROPERTY!
Percy and his friends need to complete a quest to clear his father's name as Zeus's lightning thief before the summer solstice and do it against time and nature.
Traveling across the United States, Percy, Annabeth, and Grover meet Ares in Denver, go to Vegas, and get stuck in the Lotus Hotel and Casino for 5-6 days before breaking out and continuing with only one day left to complete their quest.
You did good on your quest.
In Hades's realm, Percy stands before him with Zeus's lightning bolt is his hand. Shocked, Percy knows he is not the thief but then realizes who is.
After winning a duel against Ares, Percy returns to Camp Half-Blood. Luke invites him down to the river, then reveals himself as the true thief as the true thief of Zeus's Master Bolt.
*whispers* I was the thief... mwahah
After making amends with his father, Poseidon, Percy decides to return to New York for the school year and live with his mother and goes on with his life.