Everyone in the camp hears about the bathroom incident quickly, and everyone stares at Percy as he and Annabeth continue their tour. As they finish the tour, Annabeth tells Percy he needs to talk to the Oracle, but does not explain what the Oracle is. Percy is perturbed and wants to go home, but Annabeth tell him he is home, home at the only place that is safe for half-humans like them. She tells Percy that his father is not dead—rather, he is one of the Olympians, which makes Percy half-god. She says Percy's dad may send a sign to claim him, and that is the only way they will know for sure who he is.
Percy asks if he is stuck there forever, and Annabeth explains that some kids—like her—stay there year-round to keep safe from monsters, while others only stay for the summer. The camp's borders are sealed to keep both monsters and mortals out. She shows him a necklace she has, with one bead carved with a special symbol representing each of the years she has been there. She says the only way Percy is going to be given permission to leave right now is if he is assigned a quest.
Percy asks Annabeth about the summer solstice, something he heard both Chiron and her talk about, but Annabeth explains she does not know details, only that something major is wrong on Mount Olympus right now. She reveals that Mount Olympus hangs above the Empire State Building. She went there on a field trip with Luke and other year-rounders during the winter solstice and everything seemed normal then, but lately, the weather has been strange as if the gods are fighting.
When they finish talking, Percy heads back to cabin eleven and meets Luke, who explains that his dad is Hermes. He tries to console Percy, who is still feeling strange about the whole situation. Percy asks about the Oracle, and and Luke explains that the reason Annabeth told him to go was because Chiron told her that according to a prophecy, she would not be allowed to go on a quest until someone special came to the camp. Annabeth thinks Percy might be this special camper. At dinner, they toast to the gods and make them food offerings by dropping it into the fire. Mr. D introduces Percy to the other campers, and talks about the capture the flag tournament that will be happening soon.
Percy settles into a routine over the next few days testing out different outdoor activities but not having much success at them. Neither Percy nor the senior campers can figure out who his father is based on his skills. Percy tries sword fighting against Luke, and beats him his first try, but then loses on the second try—still, Luke thinks he has potential. Percy talks to Grover, and they discuss the empty cabins—one belongs to Artemis, who swore she would be a maiden forever, so she has no children. Hades, god of the underworld, does not have a cabin at Camp Half-Blood or a throne on Olympus.
Zeus and Poseidon have empty cabins because 60 years ago, they made a pact that they would not have any more kids, because their demigod children were too powerful and caused too many wars. Zeus broke the oath seventeen years ago, and this brought a terrible fate upon his daughter, Thalia. Zeus was forced to turn her into a pine tree as monsters attacked her on the threshold of Camp Half-Blood, and her tree still stands there today, with her spirit protecting the threshold of the camp.
The capture the flag tournament arrives, with Ares and Athena leading the teams. Percy is with the Hermes team, in an alliance with Athena. They are given actual weapons and armor to use, which surprises Percy. During the game, the Ares team attacks Percy as payback for the bathroom incident, but Percy manages to fight them off by standing in the creek, with the water reenergizing him. During this, Luke manages to grab the enemy's flag and their team wins. It is revealed that Annabeth placed him intentionally to distract the Ares team, knowing they would come after him.
As the game finishes, Percy is surprised to see that the water healed his sword cuts. Before they can think about what that means, a hellhound appears and attacks Percy, wounding him. Chiron says someone inside the camp must have summoned it. Annabeth gets Percy in the water, and it heals his wounds again. A hologram appears over his head in the shape of a trident. It is a sign—Poseidon has claimed him as his son.
Chiron moves Percy to Cabin Three, Poseidon's, and Percy is all alone. The campers steer clear of him, both because he is the son of the Sea God and because monsters are clearly attracted to him. Luke pushes Percy to train hard, and Annabeth teaches him Greek. He comes into his cabin one night to see a newspaper clipping about his and his mother's disappearance. Grover wakes Percy up the next morning and takes him to see Mr. D and Chiron. Percy guesses that Poseidon and Zeus have been fighting over something that was stolen, based on the weather, Annabeth's information, and some dreams he has been having about it. Chiron confirms that Zeus's master lightning bolt was stolen, and Zeus thinks Percy is the one who stole it on Poseidon's orders. Poseidon has been given until the summer solstice to return it, and there will be war if it is not returned.
Percy is given a quest: go find where the bolt really is, and then return it to Olympus by the summer solstice. Percy speaks to the Oracle, who tells him, "You shall go west, and face the god who has turned. You shall find what was stolen, and see it safely returned. You shall be betrayed by one who calls you a friend. And you shall fail to save what matters most, in the end" (pg. 146). After this, Chiron tells him that Hades is the only one who could have stolen the bolt, and the monsters that have been sent after Percy so far all obey Hades. Percy has to go to the underworld to retrieve it, and the gateway to the underworld is currently in Los Angeles. He cannot fly, since Zeus controls the skies, so he has to travel overland. Grover will come with him, as will Annabeth. They start packing right away.
At last Percy's father has claimed him: Poseidon. Up until this point, Percy's parentage has been foreshadowed by a number of different events, starting with the fountain at the museum in the very beginning and extending to his mother's love of the beach, their fascination with blue foods, and the bathroom incident on his first day at camp. Having Poseidon as a father sets Percy apart from the rest of the campers even more: not only is he special because he is a demigod, but he is also special because of who his father is. This specialness is complicated, though, by the fact that, because of a pact his father made, Percy was not supposed to be born. Now that this has been set up, it will certainly be a continuous point of contention.
In these chapters, the main inciting incident—the end of the capture the flag game and the hellhound's appearance—establishes the beginning of the novel's conflict. Clues, including Annabeth's talk of quests, the Big Three, and the summer solstice, have foreshadowed the quest that Percy ultimately receives. In any epic hero story, the hero's quest is the central plot, and heroes undergo a transformational journey throughout their quest. The idea is that a hero can learn more about himself when pushed out of his comfort zone into unfamiliar places, and Percy will experience exactly this over the rest of the novel.
The gods' universe contains many examples of antithesis, or direct opposites. Zeus and Hades are antitheses, as are Mount Olympus and the underworld itself. New York City and Los Angeles contain these places, as two opposing sides of the country. Right now, there seems to be a clear dividing line between good and evil: Percy, his quest, and the Olympians he and his sidekicks represent are good, while Hades, monsters, and the underworld are evil. This line will blur as time goes on.
The capture the flag game reveals much about Annabeth's characters, showing that she embodies the traits that her mother prizes. She is intelligent, coming up with a plan to distract the Ares team so her allies could grab their flag. She shows leadership and skill in battle. But her desire to be friends with Percy shows that her personality extends beyond her mother's. She acknowledges the historic rivalry between Athena and Poseidon, but she still expresses a willingness to be kind to Percy and help him on his quest.
While the children in Camp Half-Blood are demigods and heroes, it is important to remember that they at the same time, they are still human. These chapters display that through the way they isolate Percy after Poseidon claims him, showing their youthful pettiness. The dynamic of the demigods mirrors the dynamic of their parents, the Olympians. Much of Greek mythology emphasizes the Gods' humanlike and often immature behavior, and readers see some of this through Zeus's willingness to place the blame on Poseidon for the missing bolt and the two brothers' constant fighting.
Another common theme in Greek mythology is the idea of humans being assigned to do the Gods' work. Heroes like Hercules and Theseus all took on missions that were assigned to them by the gods, and Percy is about to embark on a similar task. The gods have always used their human children to do their bidding, which seems like an exploitative relationship. Percy, however, takes pride in his father, even though he has only known about him for a few days, and truly wants to clear his name, showing that he has sound motives for undertaking this quest.