The movie follows the journey of 16-year-old Percy Jackson, who has always struggled in school and seems to attract trouble wherever he goes. However, shortly after a field trip to a museum, Percy discovers that he is not a regular teenager and that his father, whom he had never met, is actually Poseidon, the Greek God of the sea.
With the help of his new friend and protector, Grover, who is revealed to be a Satyr, and his schoolmate Annabeth, who is the daughter of Athena, Percy embarks on a mission to retrieve Zeus' stolen lightning bolt and clear his name as the prime suspect of the theft. Without the lightning bolt, Zeus will declare war on Poseidon, and the world will suffer as a result.
Their quest takes them to the underworld of Hades, Mount Olympus itself, and even a Vegas casino. Along the way, Percy discovers the true power of being a demi-god and learns to harness his skills, such as controlling water, breathing underwater, and communicating with horses.
As they race against time, Percy and his friends must confront ferocious monsters and outwit devious enemies, including the treacherous Lord of the Underworld, Hades, and the cunning God of War, Ares.
In the end, Percy successfully retrieves the lightning bolt and prevents a catastrophic war between the gods. He also earns the respect and recognition of his father, Poseidon, and the other gods of Olympus. But Percy knows that his adventures are far from over, and he must prepare for more challenges in the future.