The Son of Neptune is the second novel in Rick Riordan’s The Heroes of Olympus series. Released in 2011, this novel continues the story begun in The Lost Hero, following Percy Jackson as he stumbles into the Roman demigod camp, Camp Jupiter, after losing his memory and eight months of his life. At the camp, Percy meets Hazel, daughter of Pluto, and Frank, son of Mars. Together, Percy, Hazel, and Frank are charged with a quest to free the god of death, Thanatos, from captivity to allow death to send souls to the underworld once more. Along the way, Percy regains his memory, Hazel achieves redemption for her mistakes, and Frank discovers the truth about his family legacy.

This study guide refers to the October 2011, Hyperion Books, an imprint of Disney Book Group, e-book edition of this novel.

Plot Summary

Percy is chased into Camp Jupiter by two gorgons that will not stay dead no matter how many times he kills them. Percy knows something is wrong, but he cannot say what it is, because he has lost his memory. All he knows about himself is his name and that he has a girlfriend named Annabeth. The goddess Juno tells him he will suffer the worst pain and misery of his life if he chooses to follow the path he is currently on, but Percy instinctively knows he has no other choice.

Percy befriends two students at Camp Jupiter named Hazel and Frank. Hazel is the daughter of Pluto who was rescued from the Underworld by her brother, Nico di Angelo. Frank does not know who his father is, but after his mother’s recent death in Afghanistan, his grandmother sent him to live at the camp. Before he left, she told him about a visit from Juno when he was a baby where the goddess revealed that once a specific piece of firewood burns completely, Frank will die. His grandmother gave him the piece of firewood and told him to learn to embrace not only his father’s legacy, but his family’s as well.

After Frank surprises the entire camp by leading the Fifth Cohort to victory during war games, Mars visits Camp Jupiter. Mars tells Frank that he is his father and instructs him to pick two other campers and travel to Alaska, the land beyond the gods. Frank and his team are to rescue the god Thanatos from the goddess Gaea’s son, the giant Alcyoneus. Mars tells them that monsters are rising from the Underworld at the behest of Gaea and if Thanatos is a prisoner of Alcyoneus, no one will remain dead.

Frank chooses Percy and Hazel to travel to Alaska with him. They have only four days to arrive at their destination and rescue Thanatos before another of Gaea’s sons, the giant Polybotes, arrives at Camp Jupiter to battle the camp. To give the camp the best possible chance, Frank and his friends must save Thanatos and send the Amazons to help. On the way, Frank, Percy, and Hazel stop in Portland to visit Phineas, a blind seer who knows the location of Alcyoneus and Thanatos. Phineas is plagued by starving harpies and asks Percy and his friends to capture one of the harpies for him. Instead, Percy challenges Phineas to pick one of two vials of gorgon blood, either a poisoned vial or a healing vial, and drink the contents. Percy will drink the other. Believing Gaea will protect him, Phineas agrees to the deal, writing down the location of Alcyoneus’s camp before choosing and drinking one vial. Percy drinks the other. In moments, Phineas turns to dust while Percy suffers mildly for a moment and quickly recovers.

With the information they required in hand, Percy, Frank, and Hazel continue their journey, stopping in Seattle to visit with Hylla, the queen of the Amazons and sister of Reyna, the praetor of Camp Jupiter. Hylla is struggling to keep her crown as the first queen of the Amazons has risen from the Underworld and is attempting to takeover. Hylla is not able to help Camp Jupiter while this struggle plays out, but she does give Hazel a magical horse, Arion, to aid their quest. Arion can travel at great speeds. He takes the three friends to Canada where they encounter a group of ogres outside Frank’s family home.

Frank sneaks his friends into his grandmother’s home and finds Mars sitting with his ailing grandmother. Mars tells Frank that his grandmother is dying and has been waiting for his arrival. When the older woman wakes, she tells Frank more about his family history, reassuring him that his ancestors were always on the right side even if they were not remembered that way. She then stressed that he had the same gift as his ancestors, encouraging him to discover for himself what that gift is. When the ogres begin their attack on the house, Frank believes he finally understands what the gift is, but is unsure he can do it. Instead, he uses his leadership skills to come up with a plan to get himself and his friends out of the house.

Percy, Frank, and Hazel finally arrive in Alaska, but still must get to the glacier where they believe Alcyoneus is holding Thanatos. Arion has disappeared and they take a train to the small town where Hazel and her mother once lived. Once in the town, they visit Hazel’s old home and are stranded as they cannot charter a boat or plane that will take them where they need to go. While trying to figure out their plan, a group of gryphons attacks and they are saved by Arion’s return. The horse speeds them to the glacier where Thanatos is being held. The glacier has the remnants from a Roman camp of the Fifth Cohort that went on a quest to Alaska in the 1980s and lost the Twelfth Legion’s eagle.

Percy battles the undead soldiers from the Fifth Cohort while Frank and Hazel attempt to free Thanatos. They discover that the only way to free Thanatos from his bindings is through magical fire. Alcyoneus attacks Hazel while Frank struggles with the knowledge that he has the means to free Thanatos, but it could mean sacrificing his own life. Frank lights his firewood and frees Thanatos with the fire, saving just a small nub of the firewood. When Thanatos is free, Frank helps Hazel fight Alcyoneus. They cannot harm Alcyoneus while he is in Alaska, but Frank tricks the giant into following them across the border to Canada where they can kill him.

With Thanatos free, Hazel expects to return to the Underworld, but Thanatos tells her that she is not on his list. Now that Thanatos is free, those who die will remain dead unless they can find the Doors of Death, which were left open and must be closed. Arion whisks Frank, Hazel, and Percy back to Camp Jupiter as the battle between the Twelfth Legion and Polybotes’s army rages. Percy engages Polybotes and draws him into New Rome where he convinces a small god, Terminus, to help him kill the giant. The camp celebrates when the battle ends.

Percy receives word that a warship from the Greek camp, Camp Half-Blood, is on its way. He speaks to the Romans to warn them of the impending arrival and to convince them that the Greeks only want to help with the fight against Gaea and to close the Doors of Death. Several Romans speak against working with the Greeks, but Reyna convinces the senate to hear them out. The warship arrives and Percy anxiously goes to greet them, hoping Annabeth will be onboard.