The book opens with the narrator and protagonist, Percy Jackson, warning the reader to close the book if they think they might be a half-blood because “being a half-blood is dangerous” (1). Following this, Percy introduces himself as a 12-year-old kid from New York who used to attend a school for troubled kids. Although he tried not to cause problems, things never went well for him. To illustrate his troubles, Percy recounts a field trip a year ago when things really started to go badly.

Percy’s class visits the Metropolitan Museum of Art to view an exhibit of ancient Greek artifacts. Two teachers chaperone the trip: Mr. Brunner, who drives a motorized wheelchair and is pretty cool for a teacher; and Mrs. Dodds, who is nasty to Percy. At the museum, Mr. Brunner gives a lecture about how Kronos, father of the Greek gods, ate his children and was later defeated by Zeus. Most of the kids shrug off the lecture as nonsense, but Mr. Brunner tells Percy the information “is vitally important” (7). Though he wants to learn, Percy struggles with ADHD and dyslexia, which he feels put him at a disadvantage.