The Lightning Thief uses some aspects of Greek mythology in a modern setting. It is written in a "fast-paced humorous style". in the first person and begins with Percy Jackson, a 12-year-old boy with dyslexia and ADHD living in New York City (lower Manhattan to be exact) explaining that he has been expelled from every school he has ever attended, all of them happening in very strange ways. When his class from Yancy Academy takes a field trip to the Metropolitan Museum of Art, he is told that nothing strange, unusual, or mischievious was to happen on this fieldtrip or he was going to be suspended. On this trip his friend Grover is plagued by a bully named Nancy Bobifit. Percy eventually decides to do something about this bully when the fountain he was sitting next to seemed to grab her. though he hadn't pushed, that's what she thought happened and told Mrs.Dodds his pre-algebra teacher. She then takes him away from the class to talk to him, and transforms into one of the three Furies of Greek myth and attacks him. Percy's Latin teacher, Mr. Brunner, throws to him a pen that he uncaps and a magic sword named Anaklusmos, or Riptide, appears. Without thinking Percy swings it at her and sends Mrs. Dodds to Tartarus. When Percy comes out from the battle Mr. Brunner is gone and acts like he was never there, and nobody remembers Mrs. Dodds, only a perky blond woman named Mrs.Kerr. Though he almost believes it never happened his best friend Grover seems to know otherwise.

During the last week of school, Mr.Bruner sets out a final exam, although every teacher did, this was the only one Percy studied for.Percy was studying and thought that he should go to Mr.Bruner and ask for extra help. When Percy arrived at the outside of his office however, he heard Grover and Mr.Bruner talking about him, Mrs.Dodds, and a stolen item of great importance.

When Percy and his mother, Sally, go to Montauk Beach in New York, Sally can tell something is wrong, but doesn't press Percy abbout it. Grover comes to tell them to leave immediately. A terrible storm rages as they drive to the New York countryside and they are attacked by a Minotaur. In the ensuing fight, the Minotaur takes Sally in a blinding flash of gold light. Enraged, Percy takes one of its horns and kills the Minotaur, passing out from exhaustion shortly afterwards. He wakes up three days later, healed by nectar and ambrosia, at Camp Half-Blood. Grover reveals himself to be a satyr, and Mr. Brunner to be Chiron the centaur. They explain to him that he is a half-blood, half mortal, half god.

As Percy's divine parent is unknown, he is placed in the Hermes cabin, where all the unclaimed half-bloods stay. He meets Luke, a son of Hermes; Annabeth Chase, a daughter of Athena; and Clarisse La Rue, a daughter of Ares. After several water-related incidents, a trident appears above Percy's head as his father,Poseidon, claims him.

After he is claimed a hell hound appears in camp spooking campers, as the camp was thought to be protected from monsters unless they were specially summoned. This spurs Ch iron to issue a quest to Percy to protect the camp.

The Oracle at the Camp Half Blood tells Percy that "You must go west and meet 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 fail to save what matters most in the end." Percy is told by Chiron to tell him the prophesy, but Percy only tells him the first two lines to avoid panic. Chiron interprets this as a quest to find the stolen master lightning bolt of Zeus, since Zeus blames Poseidon for stealing it. He believes that Hades has the master bolt to cause war, expand his kingdom, and take over. After defeating several mythological monsters, including Medusa,and the Chimera, Percy, Annabeth and Grover find Hades, who has taken Sally but had his Helm of Darkness (his symbol of power) stolen too. Hades also accuses Percy of stealing his helm and threatens to kill Percy and his mother and release all the dead back into the real world. Percy and his friends use magical pearls to transport themselves out of Hades' kingdom. After discovering that Ares has all the stolen items, Percy challenges him to a duel and wins, to his own surprise. When Percy presents the Helm to Hades, Hades realizes that Percy has not stolen it and returns Sally safely.

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