Percy Jackson opens by warning readers that being a half-blood is dangerous, then introduces himself as a troubled twelve-year-old at Yancy Academy, a boarding school for difficult students. He explains that field trips usually end badly for him, but he hopes this class visit to the Metropolitan Museum will be different because his favorite teacher, Mr. Brunner, is in charge. On the bus, Percy suppresses his anger while Nancy Bobofit bullies his best friend, Grover Underwood.

Inside the museum, Mr. Brunner guides the class through Greek and Roman exhibits and questions Percy about a carving of Kronos devouring his children. Percy answers part of the myth correctly, but Mr. Brunner presses him on why the story matters in real life. Percy feels frustrated because Mr. Brunner expects a lot from him despite Percy's dyslexia, attention problems, and history of poor grades.

At lunch outside the museum, Percy notices a violent storm building and thinks longingly about going home to his mother. Nancy then dumps her half-eaten lunch into Grover's lap. Percy loses his temper, and Nancy suddenly ends up in the fountain. Mrs. Dodds, Percy's hostile pre-algebra teacher, blames Percy and orders him to follow her inside, while Grover nervously tries to take the blame for him.

Alone with Percy in the Greek gallery, Mrs. Dodds accuses him of hiding something and demands a confession. She then transforms into a winged, clawed monster and attacks. Mr. Brunner suddenly appears and throws Percy a pen that turns into a bronze sword. Percy swings in panic and vaporizes Mrs. Dodds into yellow dust. When Percy returns outside, however, Nancy refers to a teacher named Mrs. Kerr instead, Grover acts evasive, and Mr. Brunner calmly insists that no Mrs. Dodds has ever existed at Yancy Academy.