The Son of Neptune
Rick Riordan
 The Son of Neptune begins with the amnesiac Percy Jackson being chased by the two remaining Gorgon sisters, who want to kill him to avenge the death of their sister Medusa. Percy, who has no memories of his past life except of his girlfriend, Annabeth Chase, manages to outdistance them and stumbles upon Juno, disguised as an old lady, who gives him two options: to carry her to the Caldecott Tunnel, into the Roman Camp and across the Little Tiber river—though she warns him that by crossing through the river he'll lose his Achilles-like invulnerability—or to retreat to the safety of the sea and live a long, happy life. Percy chooses to carry Juno in hopes of seeing Annabeth again. At the Caldecott Tunnel he meets two other demigods: Hazel Levesque and Frank Zhang. When they cross the river, Percy sees Frank get caught by the pursuing Gorgons and controls the river to destroy them. Juno then reveals herself to the people there, who are inhabitants of Camp Jupiter, the Roman camp for demigods. Percy is accepted by the camp's praetor, a girl named Reyna, and is made part of the Fifth Cohort when Hazel sponsors him. He and Hazel and Frank then prepare for the night's war games. During the games, the trio is responsible for the cohort's victory, and after the games Mars appears. He claims Frank as his son and sends Percy, Hazel, and Frank on a quest to free Thanatos, the god of Death, who is imprisoned in Alaska. On the quest, they bump into an old man named Phineas, who is all-knowing and all-seeing. He tells them that he will reveal the location of Thanatos if they capture a harpy named Ella and bring her to him. Before capturing Ella, they learn that she can memorize anything she reads and decide to gamble with Phineas instead. Phineas and Percy will each drink a vial of Gorgon blood, one of which kills while the other heals. Phineas ends up dying and the trio discover the location in Phineas's pocket: Hubbard Glacier in Alaska. On the way to Alaska, Hazel reveals that she was actually supposed to be dead but was rescued from the Fields of Asphodel by Nico di Angelo and that seventy years prior to the story she was originally started to wake up the giant Alcyoneus but stopped him from rising the day he was due to escape. At that point, Frank reveals to Hazel that his life depends on a piece of firewood that he always keeps. When it burns out, he dies. When they finally reach the glacier, they find the Roman Camp's eagle standard and most importantly, Thanatos in chains. His chains cannot be broken unless melted by the "fire of life", a.k.a Frank's firewood, so Frank starts melting the chains as Hazel attacks Alcyoneus, while Percy attacks Alcyoneus's ghost legion. Frank manages to free Thanatos with just a bit of his firewood left. Frank then goes to help Hazel and learns how to use his family power, which is shape shifting into any animal. He attacks Alcyoneus and dazes him, while Percy slams his sword at the edge of the iceberg where he was fighting, collapsing the iceberg and drowning the ghost legion. Frank and Hazel then drag Alcyoneus across the border into Canada, where Hazel kills him. Frank and Hazel meet back up with Percy in Alaska and then the trio rush back to Camp Jupiter, where, with the help of Tyson, Mrs. O'Leary, and the Roman Legion they fend off the Giant Polybotes's army. After seeing the eagle standard, the legion regains their hope and fights with renewed energy. Percy then challenges the giant Polybotes (born to oppose Poseidon) to a duel, as the rest of the camp fights the rest of the monsters. Percy calls to Terminus to help him defeat the giant, as giants can only be defeated by both a god and demigod. Percy eventually beats Polybotes after a battle using the head of Terminus' statue as a weapon. After the battle the legion names Percy as praetor, one of the two leaders of the Roman camp. Nearing the end, the groups of Greek camp demigods inform Percy of their arrival through a video scroll. He persuades the senate to trust him and let them in without a fight since the future of the world depends on both groups. Percy then resolves to introduce Hazel and Frank to his other family.