Nicole, portrayed by Melissa Joan Hart, and Chase, played by Adrian Grenier, have spent their entire lives as next-door neighbors and childhood best friends. However, their paths diverged during junior high when Nicole opted to join the popular crowd, while Chase began a rebellious streak, pulling pranks that often landed him in detention—like his infamous stunt of adding orange dye to the school's water supply and activating sprinklers at lunchtime, much to the dismay of their classmates.
As they approach their senior year, Nicole pours her heart into organizing the centennial dance for their high school, hoping to attend with her crush, Brad, who instead chooses to take a cheerleader from a rival school. Chase is in a relationship with Dulcie but finds himself dumped over what his ex perceives as a fake rebellious persona. Meanwhile, Nicole is facing the turmoil of her parents' divorce, living with her mother, Mrs. Maris, while her father, Mr. Maris, has visitation rights.
Knowing she risks being labeled a loser, Nicole asks Chase to take her to the dance as his date. He agrees, but she insists they must genuinely embrace the “dating” act to make their exes envious. Nicole completely revamps Chase's wardrobe, preparing him for the social spotlight. One evening, she phone calls him to propose their ruse of pretending to date to unleash jealousy in Brad and Dulcie, and they agree to an easy-out clause for their mock relationship, promising it can end without hard feelings.
As they navigate various events together, Chase begins to become part of Nicole's circle of friends, all while he reassures his old pals, Dave and Ray, that he hasn't really changed despite the obvious transformation. In an unexpected twist, they have fun at a club Chase used to frequent with Dulcie, allowing Nicole and Chase to bond and break down their emotional walls.
Their relationship grows deeper when Nicole intervenes to help Chase during a run-in with Dulcie and her new boyfriend, sealing their moment with a kiss that sparks jealousy rather than resentment. However, complicated emotions arise when Nicole's competitive best friend, Alicia, exploits the situation, seducing Chase in a bid to make Nicole think Chase is over her. This heart-wrenching moment leads to complications, as both Chase and Nicole grapple with their true feelings while trying to maintain their appearances with their respective exes.
As events unfold, the intertwining relationships take a toll. Chase reconnects with Dulcie, while Brad finally extends an invitation to Nicole for the dance. Yet, dissatisfaction looms over Chase's newfound romance, and Nicole ultimately rejects Brad’s offer.
On the night of the dance, feeling unaccompanied, Nicole accepts a late invitation from Ray, enjoying his company until Chase's arrival forces Ray to bow out, revealing the unspoken tension that persists between Chase and Nicole. When Chase requests a dance, he muses, “Who are we trying to make jealous now?” to which Nicole playfully responds that it’s everyone.
Finally, as the sun rises the next morning, Chase walks Nicole to his door after an eventful night, culminating in a kiss that heralds a new chapter in their lives. They unexpectedly discover that their parents have also started a romantic relationship and plan to cohabitate. Amused, Nicole suggests having a discussion about the new living arrangements in their childhood treehouse. Hand in hand, they walk into her backyard, embracing each other lovingly beneath the familiar branches, solidifying their bond.
