The story picks up with Percy at freshman prientation at Goode High School where he meets Rachel Elizabeth Dare, who helps
him recongize and fights two empousai disguised as Cheeleader, TAmmi and Kelli. Percy is forced to leave the school and
go to Camp Half-Blood, while Rachel stays behing. On the way there Percy runs into Annabeth who is annoyed that he is
with a mortal girl. When they get to camp, Percy learns that Grover is in trouble yet again but this time with the
Council of Cloven Elders for not having made progress finding the God Pan after saying he felt his presence in
New Mexico last winter. Percy also meets a middle-aged demigod named Wuintus who is the new sword instructor
of Camp Half-Blood. Chrion says he is a hard to read man that Percy and others agree with.
Quintus makes a competition and during that Annabeth and Percy find an entrance to the Labryinth. Chrion hold a council of war and it is revealed that Annabeth and Clarisse have been working together under the suspicion that Luke's plans to use this door as an invsion route. To do so, he has to use Princess Ariadne's magical string, which is assumed to be in the possession of he ancient inventor Daedalus. Annabeth is given leadership of the quest to stop Luke and chooses Grover, Percy and Tyson to help her. Chrion warns them that three heroes is the traditional number for the quest but Annabeth is shaken by her prophecy and begs for another. That night Percy gets an Iris message and learns that Nico is trying to bring back his late sister by exchanging her soul for someone who has cheated death. Percy fears Nico means him.
The next morning the four start the quest. After meeting the minor god Janus, they then meet Hera, who offers them a single wish. Annabeth wish for a way to navigate the Labyrinth and she stated that Percy knows the way. Percy doesn't know what Hero means and they begin to move on. During their quest Percy begins to suffer from nightmares about Daedalus, the Labyrinth and King Minos who is now 'living' as a advisor to Nico di Angelo. The quartet encounter the monster Kampe and her prisoner Briares. They visit the ranch of Geryon where they find Nico who is still trying to talk to his dead sister Biance and meet the god Hephaestus half way through. Tyson and Grover spilt up to go search for Pan while Percy and Annabeth go to Mount St. Helens. At Hephaestus's mountain forge, Percy confronts some telkine and is almost killed, triggers an earthquake that shooks him out a volcano.
When Percy wakes up he finds himself on the island Ogygia, which Calypso lives on. She is revealed to be the daughter of the Titan Atlas. Calyspo tells Percy she is cursed to fall in love with heros and that the Fates crash-land her on the island, even though they must leave. After another visit from Hephaestus, Percy realizes he must go home. When he finally gets back to the real world Percy finds the campers bring his shroud thinking he is dead. After an emotional visit with Chiron Annabeth, and his mother, Percy and Annabeth go to Manhattan to find Rachel Dare who being clear-sighted can see the path through the Labyrinth. They are then taken by Luke's minions and Percy has to fight Antaeus. After sparing the life of the demigod Ethan Nakamura, Percy kills he giant and escapes with the help of Quintus ice-whistle. Late he learn that killing Antaeus elimanted the last obstacle to Luke's conquest of the camp.
Annabeth and Percy then get to Daedalus's workshop where Quintus shows up and tells them that he is really the ancient inventor now a robot. Daedalus tells them that he scouted out Camp Half-Blood and believes they can never withstand a Titan assault. He believes that he needs to give Luke Ariadne's string as a part of a deal with the Titans. Then suddently they are discovered by park of Luke's army, Kelli and King Minos in the lead with Nico in chain. They questers learn that Mino has been helping Nico find Daedalus so that the inventors soul could be exchanged in order to bring back the old king of crete, not Bianca. The betrayed Daedalus and Nico fight with Annabeth and Percy to defeat the Titans. They surived and leave the inventors remains in the maze with his hellhound.
Percy and Annabeth later find the Titans fortress at Mount Othrys, where they learn that Luke has been possessed by Kronos. Ethan Nakamura joins the Titans and Nico is forced to reveal his powers to stop Krons. They run until they find Grover and Tyson who are still searching for Pan. They follow a tunnel until they get to the old god's resting place. Pan speaks to each of them, except for Nico and passes his spirt into each person presented. When they get back to Camp Half-Blood they get ready to fight. The enemy army floods out the Labyinth and lead by Kampe. Daedlus arrives as the tide begins to turn in the Titans favor, bringing his hellhound, Mrs. O'Leary and a giant Briares. Briares kills Kampe, Grove resuces Camp Half-Blood by causing a panic and the remaining campers driver the enemy into retreat. Nico helps Daedalus to pass on and thus the Labyrinth is destroyed. The inventor gives Annabeth a laptop he saved from his workshop and leaves Mrs. O'Leary to Percy. After a service is held for the dead campres and Grover is banished from the Council, Percy leaves camp for another school year.
On Percy's fifteenth birthday at the end of summer Percy gets a visit from his Father. Poseidon tells Percy of evil at work with Krons who is now in Luke's body and gives him a sand follar. Poseidon tells him to spend it wisely. Nico comes and visits Percy later and tells him the secret to deafeating Luke once and for all.