The gods of Olympus are alive in the 21st Century. They still fall in love with mortals and have children who might become great heroes, but most of these children meet horrible fates at the hands of monsters by the age of twelve. Only a few learn the truth of their identity and make it to Half Blood Hill, a Long Island summer camp dedicated to training young demigods. Such is the revelation that launches young Percy Jackson on a quest to help his real father, Poseidon, avert a war among the gods.

With the help of Grover the satyr and Annabeth the daughter of Athena, Percy must journey across the United States to catch a thief who has stolen the original weapon of mass destruction - Zeus' master bolt. Along the way, they face a host of mythological enemies determined to stop them. Most of all, Percy must come to terms with a father he has never known, and an Oracle that has warned him of betrayal by a friend.