On Percy's orientation tour to Goode High School where his mother's new boyfriend Paul Blofis is teaching, Percy is forced once against to battle monsters. Percy escapes with help from a mortal, Rachel Elizabeth Dare. Percy and Annabeth then travel back to Camp as Percy's attacker had indicated that Luke was planning an invasion
on Camp Half-Blood.
Back at Camp, all appears well though there is a sense of impending doom. The number of campers had dropped as Half-Bloods have been either killed, turned traitor or disappeared in the last 3 years. There's also a new sword instructor, a mysterious Half-Blood calling himself Quintus with a hell hound
named Mrs O'Leary for a pet.
As the campers ponder how Luke intends to attack, Percy and Annabeth stumble over one of the entrances to the Labyrinth
in the midst of their camp. With this the campers surmise that Luke intends to bring his forces in through the Labyrinth and they must start a quest to prevent Luke from finding a way to navigate the maze.
After consulting with the Oracle, Annabeth names 3 companions for her quest. Grover, Tyson and Percy.
As the 4 get hopelessly lost
in the maze, they receive unexpected advice from Hera and seek out Hephaestus.
Hephaestus agrees to help the companions find a way to the creator of the Labyrinth, Daedalus in exchange for their help. Someone has been using his forge on Mount St. Helen's but every time he tries to investigate they disappear. On the way to Hephaestus's forge, Grover finds a clue to the lost god Pan's whereabouts and chooses to abandon their quest. Tyson goes with Grover to provide him with protection.
Annabeth and Percy find Hephaestus's forge being used by Kronos's minions. Percy accidentally blows up Mount St. Helen's when attempting to evade his captors ensuring they are unable to use it further. Hephaestus reveals to Percy that to navigate the Labyrinth they need the help of a mortal
who has the ability to see through the Mist.
Percy and Annabeth then enlist Rachel Elizabeth Dare's help in order to continue with their quest.
Rachel successfully guides Annabeth and Percy to the heart of the Labyrinth where Daedalus's workshop is. Here, they unexpectedly meet Quintus who reveals he is actually Daedalus
. However, Percy and Annabeth are too late. He has given Ariadne's string to Luke granting him the means to navigate the Labyrinth. In return, Kronos has promised to make him the Lord of the Underworld once the Olympians are overthrown and reunite him with his beloved son, Icarus. As Percy and Annabeth attempt to reason with Daedalus, Luke and his army show up with Nico as a hostage. Daedalus finds that he himself has been betrayed
. Surrounded, Percy, Annabeth, Rachel and Nico escape using Daedalus's invention to fly out of the Labyrinth.
Realizing that the quickest route to return to Camp Half-Blood is via the Labyrinth, they return later. En route, they first encounter Kronos who has somehow returned by taking over Luke's body. They escape only to come across Grover and Tyson in front of the dying god Pan's cave.
Rachel leaves the group after guiding them back to New York. The rest then journey on to Camp Half-Blood. When Luke's forces finally come through, the campers are almost overrun. It is only with the help of unexpected allies that the Battle of the Labyrinth
is won. Nico, Daedalus, the Hundred-handed One Briares and Pan's gift to Grover each help to turn the tide of the battle.
Although the battle was won, many of the campers were killed. Dionysus returns with further bad news that many of the lesser gods have betrayed the Olympians. The one bright side is the destruction of the Labyrinth.
Returning home after summer camp, Poseidon visits Percy on his 15th birthday and warns Percy to take care as Typhon
, a Titan imprisoned beneath Mount St. Helens is stirring and is likely to attack New York upon waking. Nico too shows up unexpectedly later with a possible proposal to defeat Luke and Kronos.