The Sea of Monsters recap

Percy Jackson, demigod son of Poseidon, learns that the magical pine tree guarding Camp Half-Blood, formed from the dying daughter of Zeus, Thalia, has been poisoned, leaving the camp's borders failing. Chiron has been dismissed under suspicion and replaced by the cruel Tantalus. Percy discovers that his gentle friend Tyson is a young Cyclops and his own half-brother. Dreams reveal that Grover is trapped by the Cyclops Polyphemus, who guards the Golden Fleece, an object that could heal the tree. Percy, Annabeth, and Tyson set out on their own after Clarisse is given the official quest. They board Luke's ship, learn Kronos is re-forming, and escape, then pass through Circe's island, Scylla and Charybdis, and the Sirens, with Tyson briefly presumed dead. On Polyphemus's island they free Grover and seize the Fleece, and Tyson turns up alive. Getting the Fleece back to camp despite Luke's ambush, they heal the tree, which unexpectedly restores Thalia herself to life.

Previously: Percy Jackson discovered that the Greek gods are real and that he is a demigod, the son of the sea god Poseidon. He reached Camp Half-Blood, a training ground for the gods' children, and was blamed for the theft of Zeus's master lightning bolt. With his friends Annabeth, a daughter of Athena, and Grover, a satyr, he recovered the bolt, cleared his name, and stopped a war among the gods. He learned that the true culprit was his camp friend Luke, secretly serving the reviving Titan lord Kronos, who wants to overthrow the gods. Percy chose to spend the school year in the mortal world with his mother.

Percy finishes seventh grade at a new school, where his only friend is a large, gentle boy named Tyson. Monsters attack, Annabeth arrives to help, and they flee to Camp Half-Blood, which they find in crisis: the magical pine tree that shields the camp, formed from the dying daughter of Zeus, Thalia, has been poisoned, and the borders are failing. Chiron has been dismissed under suspicion and replaced by the cruel, cursed Tantalus. Tyson turns out to be a young Cyclops, and Poseidon claims him as his son, making him Percy's half-brother. Percy's dreams reveal that Grover is trapped far away by a Cyclops guarding the Golden Fleece, an object that could heal the tree. Clarisse is chosen for the official quest, but Percy, Annabeth, and Tyson resolve to go on their own.

The three set out in secret toward the Sea of Monsters, guided by Percy's dreams of Grover. Along the way they board Luke's ship, where Percy and Annabeth confront the traitor and discover a golden sarcophagus in which the Titan lord Kronos is slowly re-forming, fed by the loyalty of turned demigods. Luke reveals more of his plans and nearly captures them, but the friends escape the ship, thrown into the open water to continue their journey with the way ahead still long and dangerous.

Adrift, the travelers come to the island of the sorceress Circe, who briefly transforms Percy before Annabeth frees him and they escape. Back at sea they meet Clarisse aboard a ghost-crewed warship and are drawn into the strait guarded by the monsters Scylla and Charybdis. The ship is destroyed in the whirlpool, and Tyson stays behind at the engine and is separated from the others, presumed dead. Percy and Annabeth are flung into the sea, grieving and pressing on alone toward Grover.

The pair survive the Sirens, whose song shows Annabeth her deepest desires and nearly lures her to her death before Percy pulls her back. They reach the island in the Sea of Monsters where the Cyclops Polyphemus keeps Grover captive, disguised as a bride, and guards the Golden Fleece. In the fight for the Fleece, Tyson reappears alive, having been rescued at sea. Together the friends outwit and overcome Polyphemus, free Grover, and take the Fleece.

Escaping the island, the group is intercepted by Luke, who tries to seize the Fleece, but they get free and send Clarisse ahead to carry it to Camp Half-Blood so she receives the credit she was owed. The Fleece is hung on the poisoned pine tree and heals it completely, restoring the camp's borders. It works so powerfully that it draws Thalia, daughter of Zeus, back out of the tree and into a living body, and she awakens as a teenage girl, a return that will reshape the prophecy hanging over the eldest gods' children. Chiron is cleared and reinstated as director, Tantalus is banished, and Percy and Tyson part as brothers. Luke has escaped once more, and Kronos grows stronger.

The Golden Fleece is returned to Camp Half-Blood and hung on the pine tree, curing the poison and restoring the camp's protective borders. But the Fleece works too powerfully: it draws the spirit of Thalia, daughter of Zeus, out of the tree and back into a living body, and she awakens as a teenage girl at the base of the tree. Because Thalia is a child of one of the three eldest gods, her return has enormous consequences for the prophecy hanging over demigods of her kind, a thread the next book will take up. Chiron is cleared of suspicion and reinstated as the camp's director, and Tantalus is dismissed back to the Underworld. Percy and Tyson are reconciled as brothers, and Tyson leaves to work in Poseidon's undersea forges. Clarisse receives public credit for the quest. The larger danger remains and grows: Luke has escaped again, and Kronos is steadily gathering strength for the war to come.