They decide to travel west to reach the entrance to the Underworld, which is in Los Angeles. They meet many Greek monsters. They also meet Ares. Ares tells Percy that his mother is alive. When they come near the pit of Tartarus, Luke’s shoes try to pull Grover into it, but he escapes. Percy meets Hades, who also thinks Percy stole the Master Bolt. He also thinks Percy stole his Helm of Darkness. Percy knows that Ares has tricked him when he finds the bolt in his backpack. He runs away from the Underworld. He has to leave his mother there. Percy fights and defeats Ares by hurting the god's heel. Ares gives Percy the Helm of Darkness. Percy gives it back to Hades. Olympus is now present at the top of the Empire State Building in New York City. Percy arrives there to give the master bolt to Zeus.