The Battle of the Labyrinth
Rick Riordan
 After being attacked by empousai cheerleaders at his new school, Percy returns to Camp Half-Blood and learns about the Labyrinth; part of the palace of King Minos in Crete that was designed by Daedalus. He also meets the camp's new sword master, Quintus. During a battle drill with Giant Scorpions at the camp, Annabeth and Percy accidentally find an entrance into the Labyrinth. Percy soon learns that Luke had used this entrance before and will try and lead his army through the Labyrinth straight into the heart of Camp Half-Blood. Annabeth reads the prophecy and comes back out of the Big House with a feeling of dread. When Percy and Annabeth privately meet afterwards in Athena's cabin, and Percy asks her if she is okay, she is moved to tears and holds out her arms. Percy hugs her, telling her that she shouldn't worry about whatever she was worrying about. What Percy doesn't know is that Annabeth thinks that Percy is going to die. Using the Labyrinth, Percy, Annabeth, Grover, and Tyson, must find Daedalus to prevent Luke from obtaining Ariadne's String; the tool that would allow Luke to navigate the Labyrinth. Percy and his friends encounter Kampê (Campe), a half woman, half-dragon monster, and free her prisoner, Briares the Hekatonkheires (Hundred-Handed One), Tyson's idol. After an encounter with the goddess Hera and a battle at the farm of Geryon, the group is reunited with Nico di Angelo, son of Hades, who blames Percy for the death of his sister Bianca. Percy helps summon the spirit of Bianca, and Nico is convinced to put his grudge behind him by the ghost of his sister. The next day, however, Percy and his friends (without Nico) depart to find Hephaestus, hoping he would know the location of Daedulus. While travelling, the group gets separated, with Percy and Annabeth searching for Hephaestus and Tyson and Grover searching for Pan. After a meeting with Hephaestus, Annabeth and Percy go to Mt. St. Helens. There he finds telekhines, also known as "sea demons". He is discovered by the telkhines, who attack him. Percy finds Annabeth and they have a short argument during which Percy tells Annabeth to flee. Thinking that Percy is the one to die in the prophecy, Annabeth kisses Percy, tells him to be careful, and disappears. In an attempt to escape the telekhines, Percy causes Mt. St. Helens to erupt, pushing him out of the volcano, draining his energy in the process. When he awakens after the eruption of Mt. St. Helens, he finds himself in the mythical island inhabited by Calypso. After being treated for burns by Calypso and returning to the mortal world, Percy gets the help he needs from a mortal girl named Rachel Elizabeth Dare, who is able to see through the Mist; the magical veil that makes mortals see things differently than demigods. Grover finally finds Pan, but the god of the wild is dying and wants Grover to tell the other satyrs that they must save the natural world themselves. His spirit passes into all present, the satyr in particular, when he dies. They finally discover that Quintus, the mysterious new sword instructor at Camp Half-Blood, is actually Daedalus, who has attained extended life by putting his life-force, his animus, into a robot body and that Kronos has gained enough strength by Luke. He also possess Luke, using his body as a starter form. Kronos finds out that Nico di Angelo is a son of Hades and that he could be the child of the great prophecy, which states that a child of "Big Three" (Zeus, Poseidon, and Hades) would decide the fate of the gods. Luke has already reached Daedalus and attained Ariadne's string; using the magical instrument, he sends out Kronos's army to take Camp Half-Blood via the Labyrinth. While fighting a losing battle, the entire camp is either injured or killed, and Daedalus and Briares come out of the Labyrinth to help fight the battle and destroy Kampe. Grover rescues Camp Half-Blood by causing a Panic, which Pan had used once before, to scare away the enemy. After the battle, Daedalus sacrifices himself to close the Labyrinth, which is tied to his life. The camp say good bye to the dead, Nico leaves the camp, Grover travels trying to spread the message of Pan, Percy leaves for his 15th birthday and Nico comes by to offer him a proposal on how to defeat Kronos.