S01 E07: "We Find Out the Truth, Sort Of"
In a flashback, Sally brings Percy to a new school. Overwhelmed due to Percy struggling with abandonment and beginning to see mythical creatures, Sally contacts Poseidon, who dissuades her from taking Percy to Camp Half-Blood so he can forge his own identity. In the present day, Percy confronts Procrustes and gains access to his secret passage into the Underworld. The trio encounter Charon, who summons Cerberus. Annabeth tames the dog, allowing them to escape, but Grover realizes that he lost his pearl. In the Asphodel Meadows, Annabeth becomes stuck and has to use her pearl. After reaching Tartarus, Grover is nearly pulled into the pit by the flying shoes, with Percy then discovering the Master Bolt in his gifted backpack. Percy and Grover continue to Hades's Palace, and Hades offers to return Sally if Percy returns his Helm of Darkness, which was also stolen. Percy realizes that Kronos organized the thefts, due to his longstanding grudge against his children. Hades offers to protect them in exchange for the Bolt. Percy refuses, but promises to recover the Helm. The two use their pearls and are brought to Montauk, where they reunite with Annabeth before being confronted by Ares.