Nico is ten years old and first appears with his sister, Bianca, in a military school called Westover Hall in Bar Harbor, Maine. They are sought out by Grover Underwood, the satyr, who believes them to be two very powerful unknown half-bloods. Nico seems to be very interested in Mythomagic, a game about Greek mythology. When his sister Bianca accepts Artemis's proposal to become a Hunter, Nico gets angry at her for "abandoning" him. Percy finds Nico eavesdropping on Bianca and Zöe Nightshade (one of the Hunters of Artemis, a daughter of Atlas), and Nico makes Percy to promise to keep his sister safe. He does not appear again until the end of the book, where Percy explains to him that Bianca died to save the others on the quest. Nico creates a large crack in the ground to swallow up the skeletons that were chasing Percy. The he immediately turns on Percy, telling him he hates him, and reminds him of the oath he took to keep Bianca safe. Nico is last seen running into the woods at night, after screaming at Percy.