An action-adventure story aimed at middle school readers, Rick Riordan’s The Lightning Thief adapts the stories of Greek mythology for a contemporary setting. The journey taken by Percy Jackson—the novel's protagonist—is fast-paced, heroic, and ultimately more relevant than modern readers might at first expect.

After Zeus defeated his father Kronos and the Titans, he and the Olympians made their seat of power in Greece, the heart of Western civilization. Over the last two thousand years, that seat of power has moved from Greece to America. Now, Olympus is found on the 600th floor of the Empire State Building, while the gate to the underworld is located in Los Angeles. Unable to act directly against each other, the gods squabble indirectly by influencing human affairs.

The monsters of Greek mythology still exist as well. Although the Minotaur and Medusa were destroyed by Theseus and Perseus, respectively, they eventually returned to pursue and kill other warriors. Heroes—demigods, or “half-bloods”—that can fight these monsters continue to be born and receive heroic quests. Hercules’s trainer, the centaur Chiron, still trains demigods in a private camp found at Half-Blood Hill. Among his counselors is Mr. D, or Dionysus. At Mr. D’s command is a host of satyrs, creatures that are half-man and half-goat. Chiron and the satyrs not only train half-bloods to be heroes, but search for and try to protect them when they are young. Monsters, however, are attracted to the scent of half-bloods, so most demigods are killed before adolescence.

Menacing though these monsters may be, they cannot compete with the gods for troublemaking. It is revealed in the novel that World War II was actually fought between the children of Zeus, Poseidon, and Hades—the gods of the sky, sea, and underworld, respectively. After the war ended, these three most powerful gods swore that they would never again have children with mortals. Since then, Zeus has slipped up once. Although Zeus was not punished, his daughter Thalia was killed by Hades’s forces. Today, Zeus and Poseidon are in conflict. Zeus’s master lightning bolt has been stolen. Zeus accuses Poseidon of the theft and gives him until the summer solstice to return the master bolt. If the lightning bolt cannot be found, a cataclysmic war will be waged between the gods of the sea and the sky.

As the novel opens, Percy Jackson is twelve years old. He has never met his father, he hates his abusive stepfather, and he adores his mother. Diagnosed with ADHD and dyslexia, Percy has trouble behaving in school, especially on field trips. Percy now attends Yancy School for Troubled Kids in upstate New York. The only class that catches his interest is Mr. Brunner’s Greek mythology course, and his one friend is Grover. When Mrs. Dodds, his pre-algebra teacher, turns into a winged monster and attacks him, Percy is only just able to escape with his life. Afterward, no one can remember Mrs. Dodds, and Percy is left wondering if the attack was an illusion.

Soon after, Percy is expelled from Yancy and returns home for the summer. He and his mother go on a holiday, but Grover interrupts them, warning of an impending attack by mythological creatures. No regular student, Grover is in fact a satyr who has been assigned to watch over Percy. Percy is in desperate need of protection because very soon Percy, his mother, and Grover are attacked by the Minotaur. The Minotaur seemingly kills Percy’s mother, but Percy manages to slay the monster and drag Grover to Half-Blood Hill, the training camp for demigods.

At the training camp, Percy begins to learn the truth of his identity. Mr. Brunner is revealed to be Chiron, the hero trainer, in disguise. Mrs. Dodds is actually one of the Furies, monsters that serve Hades. Grover is actually a satyr that is assigned to protect Percy. Percy is actually the son of Poseidon. The reason that monsters such as Mrs. Dodds and the Minotaur are trying to kill Percy is that Hades is furious that Poseidon has broken his vow to stop having children with mortal women. Worse, Zeus suspects that Percy stole his lightning bolt on Poseidon’s behalf.

Although Percy suddenly finds himself surrounded by enemies, he learns that he is more powerful than he once realized. Percy proves to be an excellent swordsman, capable of defeating the best swordsman in the camp, Luke (the son of Hermes). Percy also has the ability to control and to be healed by water, and although he struggles to read English, he can read Ancient Greek quite easily.

At the camp, Percy makes friends with Annabeth, daughter of the goddess Athena. Annabeth is a cunning planner and a brave fighter. Although she is desperate to leave the camp and enter the real world, she may not leave Half-Blood Hill until the next quest is given out.

Fortunately for Annabeth, Chiron offers the next quest to Percy: find and return Zeus’s master lightning bolt. Chiron suspects that Hades is the one who stole the lightning bolt because Hades is the only one who will benefit from a battle between Zeus and Poseidon. Percy accepts the quest, hoping to rescue his mother from the underworld. Before he leaves, Percy is given gifts. Luke offers him flying shoes, and Chiron gives Percy a magical sword, Riptide, that disguises itself as a pen. He is also given a prophecy by the Oracle, which proclaims:

You will 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.

Taking Grover and Annabeth with him, Percy sets out from New York to find the lightning thief.

Along their way to Los Angeles, Percy, Annabeth, and Grover are forced to face a variety of Greek monsters, ranging from the Furies to Medusa to Cerberus. They also complete a quick mission for Ares, who gives Percy a backpack and helps him to reach Los Angeles. The trio finally arrive in the underworld where they discover that Hades has also lost his favorite weapon, the Helm of Darkness. Worse, inside Percy’s backpack lies Zeus’s lightning bolt.

Hades offers to return Percy’s mother to life in exchange for Zeus’s lightning bolt. However, realizing that they have been tricked, Percy and his friends escape the underworld and face Ares, “the god who has turned.” Using his power over the sea, Percy defeats Ares in battle and reclaims the Helm of Darkness, which he promptly returns to Hades. Percy returns to New York and Olympus, where he returns “what was stolen” to Zeus. Back at home with his mother and stepfather, Percy considers saving his mother from his abusive stepfather, but chooses instead to let her save herself. In this way, he “fails to save what matters most” by choosing to allow his mother to rescue herself from her abusive marriage.

Back at Half-Blood Hill, Percy discovers his betrayer, Luke. Leading Percy into the woods, Luke tries to kill Percy using a scorpion. Luke explains that Ares was a pawn of Kronos, and Luke has become Kronos’s servant. Although Percy survives the bite of the scorpion, it is clear that things are hardly over for Percy Jackson and the Olympians.