In The Sea of Monsters, a 13-year-old demigod Percy Jackson goes on a quest with his friend Annabeth, a daughter of Athena, and Tyson, a Cyclops, who happens to be Percy's half brother. They go to save Thalia's pine tree, which has been poisoned mysteriously , and to save Grover, Percy's best friend. In order to get the Golden Fleece, which will heal the tree, he must travel across the omious Sea of Monsters to an island guarded by the Polyphemus and his man-eating sheep, where his friend Grover is trapped. Throughout the journey, Percy, Annabeth and Tyson face many challenges, such as the Sirens, Scylla, and Hydra. During the climax of the book the trio fights with Luke, an old friend. Back at camp, since Thalia's tree is injured, the magical borders of Camp Half-Blood have been going down, allowing monsters to enter the camp. Chiron has also been suspected as a perpetrator, and replaced by the extremely antagonistic Tantalus, who was cursed to an eternal fast for serving his own children at a feast for the gods. In the end, Percy rescues Grover, defeats Polyphemus (with help from Tyson, who was thought to be dead by that time), and retrieves the Golden Fleece. Chiron is re-hired and everything seems to be perfect. When they return to camp, the camp places the Fleece on the tree. The next day, Grover awakens Percy to find out that the Golden Fleece also brought Thalia back to life. Giving Kronos another chance to control the prophecy.