After discovering that monsters are real on a school field trip, young Percy Jackson is forced to flee from his home along with his mother and best friend.
Percy tries to settle in to his new life at Camp Half-Blood, where new friends – and foes – are preparing for a camp-wide competition that could give Percy a chance to prove himself.
After Percy recruits Grover and Annabeth for a quest to the Underworld beneath Los Angeles, the three escape an attack on the road and seek refuge in the home of Medusa.
When Percy is poisoned by a young chimera he and his friends seek help at St. Louis's Gateway Arch, a temple to Athena – though Annabeth is worried that her mother may not protect them.
After a chance encounter the god Ares tasks Percy and Annabeth with retrieving his shield from one of the other gods, threatening to put an end to their quest for the Master Bolt as a larger war looms.
Percy and his companions make their way into the Underworld, where mortal dangers lie between them and Hades' palace – and a surprising discovery about their quest.
In an effort to stop a war among the gods Percy must defeat Ares and plead his case directly to Olympus, knowing that his own mother's life also hangs in the balance.
