When Percy and his friends get to LA, California they head towards the entrance to the underworld. When they got to the entrance, they met Charon (the ferryman of Hades). After Percy paid him, Charon took them down into the underworld so that they can confront Hades for stealing the lightning bolt.
THE ROAD BACK
Once they reached the underworld, they were confronted by Cerberus and to distract him from not eating them, Annabeth pulled out a red rubber ball. Then they found out that Hades own Helm of Darkness was missing and that the Lightning Bolt magically appeared in Percy's backpack given by Ares. After escaping Hades wrath by using the pearls, Percy battles Ares on the Beach
After fighting Ares, Percy got the Zeus's Lightning Bolt and Hades Helm of Darkness.
After defeating Ares and getting the lightning bolt back, Percy and his friends get on a plane to fly to New York to get to Mount Olympus on time to return the lightning bolt to Zeus and to meet his father Poseidon for the first time.
Percy gets to Mount Olympus just in time and returns the lightning bolt to Zeus. He tells Zeus and Poseidon of the darkness in Tartarus that influenced Ares to steal the lightning bolt.
Percy and his friends has returned to Camp Half-Blood without dying while saving his mother and returning the lightning bolt to Zeus.