Aboard Clarisse’s undead Confederate ironclad, Percy, Annabeth, and Tyson are treated as unwanted guests and told they are banned from returning to camp. Clarisse refuses Annabeth’s plea to work together against Luke because she is determined to win the quest alone and prove herself. Percy realizes Clarisse is hiding part of the prophecy, and after she orders the three of them confined below, the tension between pride and cooperation becomes the chapter’s central conflict.

While asleep, Percy dreams of Grover on Polyphemus’s island. In the dream, Polyphemus discovers Grover has been unraveling his wedding dress, then takes him outside and unintentionally reveals the island’s layout, the Golden Fleece hanging on a tree, and the rich magic surrounding it. Grover also learns that Polyphemus has a “state-of-the-art security system” and is forcing him to finish the wedding train by the next day, which raises the urgency of any rescue.

Percy wakes to alarms as the ship nears the entrance to the Sea of Monsters. Before reaching the deck, Percy secretly overhears Ares berating Clarisse through a steaming vision and threatening her if Percy steals the quest, which explains Clarisse’s fear and stubbornness. On deck, Clarisse identifies the passage between Charybdis and Scylla as the only way forward and chooses to attack Charybdis head-on rather than risk Scylla.

As the Birmingham enters Charybdis’s pull, Percy cannot control the sea, and Tyson warns that the engine is failing from the strain. When the boiler room begins to overheat, Tyson volunteers to go below because his Cyclops nature protects him from fire and because he understands machinery. Clarisse’s cannons damage Charybdis only slightly, but Tyson manages to steady the engine long enough for the ship to resist being swallowed.

Charybdis then spits the ship away, sending the Birmingham toward Scylla’s cliffs. The engine is still about to explode, Tyson remains trapped below, and Scylla begins snatching sailors from the deck with lightning-fast heads. Annabeth and Clarisse try to launch lifeboats while Percy tries to reach Tyson, but Scylla grabs Percy and drops him only after he stabs one of her eyes.

Percy falls as the Birmingham explodes beneath him, apparently killing Tyson and destroying the ship. Annabeth opens Hermes’s wind thermos to blast the lifeboats and Percy away from the wreck, preventing an immediate death but scattering everyone. Percy crashes into the sea, grieving Tyson and believing his half-brother is gone forever.