After a harrowing experience at his school trip, Percy Jackson returns home for the summer vacation, wherein he and his mortal mother Sally Jackson, travel to their cabin in Montauk to take their mind off things. However, the trip is cut short after a series of harrowing incidents, such as being attacked by the Minotaur. Percy finds himself at Camp Half-Blood, a training camp for demigods like him. He discovers that he is a demigod, son of Poseidon, the Greek god of the sea, earthquakes, and father of all horses, (which he made from sea foam). Percy also learns that his best friend, Grover Underwood, is actually a satyr (a half-goat, half-man), and that the Greek gods are accusing Percy of having stolen Zeus' master lightning bolt, the most powerful weapon in the world. To clear his name, save the world from another war between the Olympian gods, and maybe even save his mother, Percy sets out to retrieve the lightning bolt from Hades, who is suspected of being the real thief. Thus, Percy, Grover, and Annabeth Chase, a daughter of Athena, start on a journey to the underworld, facing numerous mythological monsters on the way. After confronting an innocent Hades, they learn that their friend Luke Castellan, son of Hermes, is the real thief who stole the bolt to allow Kronos, the defeated king of the Titans, a chance to rise again.