At the opening day of the senior year for the gang of Bayside High, Zack and Slater compete with each other over a pretty new transfer student from Idaho, named Joanna, and the guys feud comes to physical blows between them over who will take Joanna to the Senior's Dance at the Max. Meanwhile, Lisa becomes smitten with a new student named Darren, not realizes that he's a freshman, while Mr. Belding decides to change his own image by wearing a wig.
Screech's invention of a new spaghetti sauce wins him the admiration of a snobbish Beverly Hills rich girl, named Robin, while Zack and the rest of the gang makes a show for a cable access for a communications class in which Mr. Belding is teaching the class.
Tori Scott, a tough, wise-talking, black leather-clad transfer student arrives at Bayside and she and Zack don't hit it off when Tori threatens to undermine Zack's seniority. But Zack and Tori are reluctantly paired for a class ad project, as well as helping Lisa plan the school's annual Fall Ball. Meanwhile, Lisa alienates the dance committee, until Tori comes to her rescue with taking over the planning the proves herself to the gang that she can be cool.
Zack helps Lisa put together a fashion show to get her into FIT. An unexpected kiss leads them to decide they want to be more than just friends, but when Screech finds out, he sabotages the fashion show and challenges Zack to a fight.
Tori and Lisa form a Bayside "Teen-Line" as a community service project in which Zack reluctantly joins and he becomes close to Melissa, a disabled girl in a wheelchair whom he becomes overprotective which begins to alienate her to the most extreme. Meanwhile, Screech takes under his wing a wild young boy for another troubled student.
When Zack gets yet another after-school detention for using a cell phone on school grounds, he tries to sneak out, for just a while away from Mr. Belding, so he can appear on a radio call-in show at the Max and win a trip to Hawaii. But instead the whole gang ends up in detention with him after many failed attempts to get him out.
Slater and his military officer father fight over where A.C. will attend college, and Zack intervenes to fix it by attempting to impersonate Slater during a visit by a visiting congressman. Meanwhile, Jessie worries about college acceptances that she may be rejected by each one, whereas Screech learns he's been accepted to every college he's applied to for his good grades.
For their science project, Screech and Kelly construct a machine which is supposed to reveal the compatibility between two people. It causes problems, however, when it seems to confirm Jessie's suspicion that Slater still has feelings for his old girlfriend, Jennifer, who has just moved to town. To add even more complication, Zack develops a crush on Jennifer, but she's still preoccupied with Slater.
Zack seems to get a great deal on senior rings for the class. But his dealer turns out to be a con artist and a fake, so Zack asks Screech to dress up as "Ninja Screech" to pull off a scam of their own. Meanwhile, Tori bets with Lisa that she can go to a movie with Screech and not be mean to him. But Tori gets more that she bargained for when Screech falls for her.
The school fights over how to spend the money that an alumni leaves the school when the Zack, Slater, Screech, Ox and the rest of the guys want the money for the boy's sports while Lisa, Tori, Ginger, and the rest of the girls want it for the girl's sports. So, Mr. Belding decides to settle the conflict by having a sports competition between the boy's blue team and the girl's red team. But Zack resorts to unethical tactics when he sabotages the girl's bake-off contest, and when the girls find out, they plan their revenge leading to an all-out war of the battle of the ...
Slater gets upset when his younger sister J.B. starts dating Zack before a 1950s Sock Hop at the Max. So, Slater tries to break them up setting up a double date between Zack and J.B., and him and Tori at the movies to prevent anything from happening. Meanwhile, Mr. Belding tries to make the boys get in touch with their male sensitivity by having them attend a "sensitivity class".
Hijinks run all-round before the last dance of the school as the gang tries to raise money to hold their Senior Prom. But with the gym decorated for a play, Zack proposes a Western-themed square dance. Meanwhile, Zack tries to get Kelly to go with him as a date while Screech tries to find any date, until Lisa feels a little compassion and decides to attend with him. At the dance, Kelly is pursued by student Matt Wilson, while Slater and Jessie end up locked in the boiler room.
Zack creates a "Girls of Bayside" video dating tape to make enough money to buy a car for himself, but with massively unexpected results when Screech accidentally creates the video using the video yearbook, in which everyone wants Zack's hide.
The gang forgets Screech's birthday! To make it up to him, they intend to throw him a surprise birthday party in Mr. Belding's office! With all the sneaking around in the hallways, Screech, as the new, bitter hall monitor, sends all his friends to detention. Will they be able to pull it off before Mr. Belding returns from looking for a lost student at the mall?
Zack and the gang throw a baby shower for an expectant Mrs. Belding in an attempt to avoid taking a mid-term. But things take a turn when a massive earthquake strikes Bayside in which Screech and Mr. Belding get stuck in his collapsed office, but Zack and Tori get stuck in an elevator with Mrs. Belding who goes into labor.