On the first day of school, Miss Carrie Bliss intervenes on behalf of a troubled new student and tries to balance her personal and professional lives. Meanwhile, her new husband, Charlie, struggles to accept her devotion to her career.
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.
Screech asks Zack to write a love note for him to give to Lisa in exchange for writing his term paper. Miss Bliss inadvertently discovers the note and general chaos ensues when she thinks Zach wrote it for her. Then, Mr. Belding finds it and thinks Miss Bliss wrote it for him, then Tina finds it, and so on leading to general chaos.
After Zack breaks his Dad's $300 video camera, he asks Mikey to help him scam enough money to buy a new one before his father finds out. When Miss Bliss current history topic is the stock market, Zack sees a chance to making it big and deceives Miss Bliss into investing a high-risk stock involving potatoes and when the stock drops, it costs Miss Bliss a lot of pocket money.
Nikki refuses to do Mr. Morton's science class which includes dissecting frogs. So she, aided by Zach, Lisa, Mickey and Screech releases them, which makes things worse instead of better. Meanwhile, Mr. Belding tries to be friendly to Miss Bliss after mistakenly thinking that she has received an offer for a teaching position at another school.
Zack and the gang encourages Screech to stand up to a 9th grade bully named Deke Simmons, unaware what causes the guy's rough exterior in which Miss Bliss learns that Deke is illiterate. Meanwhile, Lisa and Nikki are arguing over how to perform in Nikki's school play while Tina and Milo argue over the use of the school stage.
Zack and Mikey's friendship threatens to come to an end over a girl whom Mikey likes, but who asks Zack to the school dance. Meanwhile, Mr. Belding is wary about holding the school dance because of the threat of violence from the students while Miss Bliss crashes it with her latest dancing beau.
Zack and Nikki are fighting when then they're partnered for a class project making things worse for both of them. Meanwhile, Tina moves in with Miss Bliss after her boyfriend dumps her and she quickly drives Miss Bliss crazy.
Zack bets with Nikki that he can kiss a 17-year-old pop singer, named Stevie who is giving her final performance at J.F.K. So, Zack pretends that he's dying to get it and fools nearly everyone... except Miss Bliss who knows Zack's reputation as a compulsive and pathological liar. Meanwhile, Stevie stays with her favorite old teacher: Miss Bliss.
Zack is invited into joining a "cool club," by two high school guys, unaware that he is the victim of a prank, which nearly costs him his friends when he's forced to bully and humiliate them. Meanwhile, Miss Bliss becomes principal for the week and Mr. Belding gets to teach her class.
The unorthodox teaching methods of Miss Bliss' former history teacher comes to conflict with Mr. Belding when he is brought in to substitute for her. Meanwhile, Nikki is the star pitcher for the JFK's softball team, but has second thoughts when Lisa tells her to get in touch with her "domestic side."