Trama

Percy sets off on the quest to return Zeus' bolt and stop a war between the gods.

Percy is sent to the attic of the main house to see the oracle Delphi, who, using the visage of Percy's stepdad Gabe, gives him a prophecy that he will reclaim the Master Bolt from the god who has turned against his brethren. With the quest legitimized by the oracle, Chiron lines up the most qualified campers so Percy can choose his two quest companions. Percy immediately chooses Annabeth, telling Chiron that he wants someone who won't hesitate to do what must be done if the quest requires it. He also chooses Grover, who is on a punishment detail since going against Mr. D. Grover doesn't understand why Percy would want him on the quest, and Percy doesn't tell him that Delphi also prophesied he would be betrayed by a friend, just telling Grover that he trusts him the most. Percy packs to leave, having been supplied with human money as well as golden drachmas, the currency of the Olympian world. Luke comes to give him a pair of winged shoes he was gifted from his own father Hermes, and Percy confides that he thought about choosing Luke as his second questmate, but was afraid that if the chance comes to rescue his mom, and it complicates retrieving the bolt, Annabeth may try and stop him, and Luke would be on her side. Luke understands, and asks Percy to watch out for them. As the trio leave, Annabeth stops at the pine tree that marks the edge of camp. Grover explains that the tree is where Thalia was struck down while covering Luke and Annabeth's sprint to safety, holding off a group of monsters sent by Hades, including the fury who attacked Percy, Alecto. Thalia stayed behind to fight, against the protestations of her assigned satyr protector. Before Thalia could die, Zeus turned her into a tree that would strengthen the borders of the demigod sanctuary. Percy is unimpressed by Zeus' solution to 'save' his daughter, which annoys Annabeth. She takes charge of the group, telling Percy to follow her lead if he wants to survive. They make their way to the city and take a bus out of town. Percy doesn't understand why they are traveling via a slow, smelly bus all the way to Los Angeles where the entrance of the Underworld is if their quest is so important, instead of taking a plane. Grover tells him that as a forbidden child, Percy has a target on his back from monsters and gods alike. Zeus may very well try to kill Percy himself, and the sky is his domain. Staying on the ground is their best chance to avoid his wrath, and the smell of the bus should help hide them from monsters. They stop at a gas station and Annabeth leaves to restock their snacks. She insists Percy stay on the bus, and they argue about her assumed authority on this mission. Grover attempts to defuse the situation by singing a satyr song of consensus, but only succeeds in annoying them both into silence. While inside, Annabeth detects one of the Furies, and and finds Alecto/Mrs. Dodds on the bus. She puts on her invisibility cap and quietly confronts her. They spar verbally before Annabeth demands to know why she and the other fury are skulking about, and Alecto tells her they have been sent to retrieve Percy, alive. She offers Annabeth a deal; lure Percy outside where they can take him quietly, and Annabeth and Grover can continue the quest unimpeded. Annabeth silently returns to the others and warns them of the danger, as Alecto and her fury sister transform and attack. Annabeth kills the second fury and Percy and Grover activate the fire alarm, causing Alecto to get blocked by the evacuating passengers while the trio escape into the forest.

Grover leads them to a secret Satyr path through the woods, which was used by his Uncle Ferdinand who went on a quest of his own years ago, and never returned. Percy says they need to contact camp for help, but Annabeth insists that encountering danger is simply part of going on a quest. Percy is uninterested in continuing blindly for the sake of glory, and Annabeth asks him why he is afraid of accepting who he is, reminding him he is more than just a kid. Percy suggests they at least call her mother, Athena, to help them. When Annabeth balks at the idea, Percy realizes that none of the gods are in regular contact with the half human children. They continue arguing as Grover tries ease the tension, and Annabeth lets slip that Grover was her protector before he was Percy's, and Percy realizes that his friend was the protector who failed to save Thalia. Before they can continue fighting, Grover suddenly smells someone cooking hamburgers in the middle of the wilderness. They follow the smell to the seemingly desterted Auntie Em's Garden Gnome Emporium and Cafe, where they find a large statue garden. Annabeth is suspicious, and soon they find perfect statues of real monsters. Realizing who lives here, they try to retreat, but Alecto has caught up with them. She chastises Annabeth for not taking her deal, but they are stopped from fighting by the emporium's owner, Medusa. She knows who the two demigods and their satyr friend are, and invites them inside for food and to talk. The fury shrinks back, but will not leave without her prize. Percy suggests they go inside, thinking they can trust her as his mother was always sympathetic to Medusa's story, and she may not be as evil as people think. Annabeth is unconvinced, but with no other choice, she follows them in. Medusa welcomes them, though Annabeth is concerned she is more at risk than the others in this case. Medusa assures her she does not hold a grudge against the girl simply because she is Athena's daughter. As they eat, Percy asks what Medusa is, if she isn't a monster, yet is powerful enough to strike fear into the monster outside. The woman claims that she cannot stand monsters, and claims her power to deal with them permanently is a gift from the gods. Annabeth reminds her that it was a curse, one placed on her by Athena. Medusa admires Annabeth's loyalty to her mother, telling her that when she was mortal, she was once a devout worshiper of Athena, content to serve her without recognition forever. However, Poseidon saw her and fell in love with her, and in jealousy, Athena cursed her to never be looked at again. Annabeth says that isn't what happened, that her mother is just, but Medusa says that all gods are bullies, blaming mortals for their own mistakes. Annabeth calls her a liar, and Medusa goes to the kitchen to prepare more food, asking Percy to join her. Feeling sorry for her, he goes and apologizes for Annabeth's behavior. She tells Percy the girl will betray him, as she was betrayed by Athena. Percy insists she wouldn't, and asks why she's so interested in keeping him safe. She says that she feels kinship with his mother, who she says is in danger because of Poseidon's negligence. She tells him his companions will try and stop him if he deviates from their quest to save his mom, and offers to 'remove' Annabeth and Grover so he can finish his quest. When she turns, Percy has already run for it. Angered, she takes off her veil and pursues.

With the fury still outside, the trio meet up and flee into the basement, finding a vast cavern with hundreds of human statues, Medusa's victims. She enters the basement, and the three kids run into the maze of statues. Grover tries to use the flying shoes to distract her, but accidentally flies off into the darkness, leaving Percy and Annabeth on their own. They hide as Medusa approaches, who tells them they have made their choice to side with their parents against her, mocking Percy that he could have saved his mother if he had listened to her. Percy draws his sword and closes his eyes as she finds him. Before she can kill him, Grover crashes next to them, drawing her attention while Annabeth puts the Yankees cap on her. As the cap turns her invisible, Percy is able to cut her head off. They regroup and find the invisible head, and Percy and Annabeth take it upstairs. Percy goes outside, and uses Medusa's head to turn Alecto to stone when she charges at him. The two return to the basement and find Grover, who has discovered the petrified body of his uncle among Medusa's victims. Percy suggests keeping the cap on the head and burying it to ensure no one will ever stumble upon it, which Annabeth reluctantly agrees to, before demanding to know what Medusa meant by saving Percy's mom. He wants to know what "offer" the fury made to her, and they begin arguing again. Grover snaps at them both, telling Percy that the hat is the only thing she has from her mother, and tells Annabeth that Percy's mom is alive and being held in the Underworld. He asks them both to have sensitivity towards eachother's situations, and asks Percy once again what it is he seems so scared of. Percy finally admits that the oracle warned a friend would betray him, so he picked Annabeth for the quest because she would never want to be his friend, and he picked Grover because he thought he could trust him no matter what. However, ever since they began the journey he has felt alone and confused. Annabeth tells them that Alecto offered to let her and Grover go if she turned Percy in, and Percy tells her that Medusa said she would help get Percy's mom back if he let her have the other two. Having come clean to eachother, Grover says they need to commit to working together as a team from now on if they are to have a hope of completing their quest. Percy decides to use the Hermes Express postal service that Medusa used to ship her statues to send her head to Olympus. Grover and Annabeth warn that the gods won't take it well, but Percy argues that between Medusa trying to stop their quest to prevent war, and her conflict with Athena, they might see it as a tribute. And this way, Annabeth can keep her mother's hat.

Later, at the Empire State Building in New York City, Hermes happily delivers the package with Medusa's head to Mount Olympus.