Percy Jackson has had a difficult life. He has been diagnosed with attention deficit–hyperactivity disorder and dyslexia, and he has been expelled from several schools—once for firing a cannon during a field trip. Percy and his best friend, Grover, are on their way to another field trip when Rick Riordan’s The Lightning Thief begins. When Percy gets into trouble on the trip, his teacher, Mrs. Dodds, takes him aside. When they are alone, Mrs. Dodds turns into a gigantic, leathery creature and attacks him. Percy’s wheelchair-bound Latin teacher, Mr. Brunner, tosses a pen to him. In Percy’s hands, the pen turns into a sword, and he defeats his monstrous teacher. However, when Percy returns to class, no one else claims to have any memory of Mrs. Dodds; their teacher is Mrs. Kerr, whom Percy now meets. Percy is expelled from this school. As he leaves, Mr. Brunner claims that it will be for the best.

Before he can return home from upstate New York, Percy sees three monsters holding a ball of string. They cut the string in half. When Percy mentions this, Grover rushes him onto the bus. Along the way, he claims that he is meant to protect Percy, which is ironic because Percy usually considers himself Grover’s defender. Nevertheless, Grover makes Percy promise to stick by him. However, when Grover stops to use the washroom, Percy sets off on his own.

Percy is unhappy with his home life. He is devoted to his mother, but he has never met his father. Percy hates his step-father—the cigar-smoking, poker-playing Gabe Ugliano. Gabe even takes Percy’s cash so he can gamble with it. When his mother comes home, she tells Percy that they are going to go stay in a cabin on the beach in Montauk. At first, the trip is delightful, but things start to go wrong quickly. Grover, who is actually a satyr, finds Percy and his mother. Another monster is about to attack. Percy’s mother collects the boys and they drive away. She is taking Percy to a safe place.

Their trip is interrupted when they are attacked by the Minotaur. Grover is knocked unconscious during the attack. They are now alone in the outdoors with this monster. It cannot see or hear very well, but once it catches a person’s scent, it will charge. There is a flash of light and Percy’s mother disappears. In retaliation, Percy attacks the Minotaur, clambers onto its shoulders, and manages to tear off one of its horns. Percy uses the horn to the defeat the monster before dragging Grover into the woods.