The Lightning Thief is a 2005 fantasy-adventure novel based on Greek mythology, the first young adult novel written by Rick Riordan. It is the first novel in the Percy Jackson & the Olympians series, which charts the adventures of modern-day twelve-year-old Percy Jackson as he discovers he is a demigod, the son of a mortal woman and the Greek god Poseidon. Percy and his friends Annabeth Chase and Grover Underwood go on a quest to prevent a war between the gods Zeus, Poseidon, and Hades.