Jessica Spencer (RACHEL McADAMS) is one of the most popular girls in high school. Not only is she the head cheerleader, but she also has a faithful and loving boyfriend in Billy (MATTHEW LAWRENCE) as well as what seems like a strong family unit consisting of mom, Carol (MELORA HARDIN), dad, Richie (MICHAEL O'KEEFE) and younger brother, Booger (MATT WEINBERG).
Yet, Jessica isn't the nicest person in the world and it isn't above her to make fun of fellow classmates Hildenburg (MEGAN KUHLMANN) and Eden (SAMIA DOUMIT). Accordingly, but by accident, she gets her comeuppance when an ancient spell causes her to unknowingly switch bodies with Clive Maxtone (ROB SCHNEIDER), a grubby 30-year-old criminal.
Panicking, she goes to her best friend, April (ANNA FARIS), for help, but April freaks out upon seeing the disgusting older man. After a bit of convincing, April and their friends Lulu (ALEXANDRA HOLDEN) and Keecia, a.k.a. Ling-Ling (MARITZA MURRAY), try to figure out what to do regarding this unusual predicament, while Clive, now looking like Jessica, does the same.
Meanwhile, Jessica also tries to make herself look better as a woman inside a man's body, which eventually attracts April's romantic attention despite having a boyfriend, Jake (ERIC CHRISTIAN OLSEN). That causes her mom, Julie (LEILA KENZLE) to worry about her, much to the chagrin of her father Stan (ROBERT DAVI)
At the same time, Jessica - looking like Clive - ends up being mistaken by Jessica's dad as the new gardener, and then later gets a job as a janitor working for Vice Principal Bernard (LEE GARLINGTON).
With time running out before prom and the big cheerleading competition, Jessica and her friends try to figure out if rival Bianca (MARIA-ELENA LAAS) or someone else is responsible and how to reverse the switch.