Percy, Annabeth, and Thalia are sent to rescue two half-bloods, Bianca and Nico Di-Angelo. While on this mission, they are attacked by a manticore, but are saved by the Hunters of Artemis. Annabeth is taken captive when the manticore flees. The Hunters, Percy, Thalia, and Grover are sent to camp by Artemis and Apollo. Artemis is soon taken captive and a quest is issued. Grover, Thalia, Bianca and Zoë Nightshade, Artemis's lieutenant, go to rescue Artemis. Percy follows and soon joins the quest. Bianca is killed while facing an automaton. They learn that the Titan Atlas has escaped and was behind the kidnapping of Artemis. Atlas is defeated and returned to holding the sky, but Zoe is killed by Atlas who is her father. Thalia replaces Zoë as Artemis' lieutenant during the gods' summit. Thalia's induction as a lieutenant of Artemis ensures that she never reaches 16, thus escaping the prophecy but leaving Percy as the only one who can fulfill it. They return to camp and Percy informs Nico about Bianca's death. He blames Percy, accusing him of failing to protect her and runs away. Percy learns that the underworld god, Hades, is Nico's father.