Percy Jackson learns that Camp Half-Blood is in danger after the magical barrier, protected by Thalia’s tree, begins to weaken. With Annabeth and his new half-brother Tyson, Percy goes on a quest to rescue his friend Grover, who is trapped in the Sea of Monsters.
To save him and protect the camp, they must find the Golden Fleece, a powerful magical object capable of healing the poisoned tree. During their journey, they face many dangers such as Circe, the Sirens, and the Cyclops Polyphemus.
In the end, they succeed in rescuing Grover and bringing back the Golden Fleece. The camp is saved, but a bigger war involving the Titans is coming.