During the first day back of the new school year at J.F.K. Junior High, preppy and pathological liar Zack Morris runs into a 9th grade student, named Karen, to whom he had lied about his age earlier that summer in order to get to know her better. He persuades classmates Mikey, Screech, Tina, and Nikki to help with his charade. Meanwhile, Miss Bliss tries to squeeze a dinner date into her new schedule with her new boyfriend Brian, the doctor.