After learning that he is the son of a mortal woman and Poseidon, god of the sea, twelve-year-old Percy is sent to a summer camp for demigods like himself, and joins his new friends on a quest to prevent a war between the gods.
When Apophis, the chaos snake, threatens to plunge the world into eternal darkness, siblings Carter and Sadie Kane plan to use an ancient spell to destroy the snake, but first must rely on the murderous ghost of a powerful magician.