After overhearing a phone call during which a man named "Esposito" orders someone to murder a child before he can testify against him in court, Jarod "Brody" infiltrates Bolton Elementary School, in Bolton, Minn. Posing as a substitute teacher for the fifth grade, Jarod races against the hit man, trying to discover which of the students is the child who witnessed Esposito murdering someone.
Jarod's search is ended when a chance encounter in the school hallway confirms that Eric is the boy who witnessed the murder while he was on a field trip from Woodbury Elementary School. Jarod knows he must find the hit man, or Eric will never be safe, no matter where he goes.
By hacking into the federal marshals' database, Jarod determines that the school counselor, Rachel Daly, is actually a federal marshal assigned to the witness protection program, but currently listed as "on leave." Realizing that the hit man is actually a woman, Jarod seeks out Eric, only to find that Ms. Daly has already delivered him into the hands of Esposito. Jarod rescues Eric. Daly and Esposito end up in the pit in which they planned to bury Eric. Jarod turns on the machinery so that the pit begins to fill with cement. Not knowing that the police are on their way, Daly and Esposito think that Jarod intends to kill them, and they confess all.
Before leaving, Jarod helps Eric even the score with Joel, a bully who has been tormenting him. After lacing one of Eric's brownies with prune extract (knowing that Joel will take it from him), Jarod rigs the door to the portable bathroom on the playground to fall off while Joel is in there-exposing him to all of the other students. He also gives Eric the courage to tell the girl of his dreams how he feels about her.
During his Pretend as an eligible man in a small town, Jarod quickly finds himself inundated with casseroles prepared by his students' single mothers. He also discovers the joy of corn dogs.
At The Centre, Miss Parker discovers that Mr. Raines has been keeping his wife, Edna, sedated for the past 20 years at the Pratt Institute. Because Edna and Catherine Parker worked together at The Centre, Miss Parker thinks that Edna might have some of the answers that she's been seeking. Before she can contact Edna, however, Edna contacts her-by escaping the Institute and arriving at Miss Parker's door.
Twenty years under sedation have taken their toll on Edna. Confused most of the time, Edna believes Miss Parker to be Catherine. She realizes who Miss Parker is for only one brief moment, during which time she explains that she came because she was hoping Miss Parker would finish Catherine's "Mirage" project. While Miss Parker is at The Centre, urging Broots to find anything he can about "Mirage," Edna slips out of the house through a back window, boards a bus and exits Miss Parker's life as suddenly as she entered it.