Once upon a time, way back in 2002, Marni (KRISTEN BELL) was the high school wallflower. With braces, unfashionable glasses, acne and a bad haircut, she was practically invisible, except to Joanna (ODETTE YUSTMAN), known as J.J. back then, who routinely tormented her, what with being the self-proclaimed warden of the school.
Since then, Marni has grown up into an attractive young woman who turned her past grief into becoming a confident success in the PR world. That's about to change when she learns that her older brother, Will (JIMMY WOLK), is about to marry Joanna, unaware of her past bullying of his kid sister. Such past behavior is also unknown to Marni's parents, Gail (JAMIE LEE CURTIS) and Mark (VICTOR GARBER), younger brother Ben (BILLY UNGER) or Grandma Bunny (BETTY WHITE).
They all love Joanna for the compassionate, socially conscious young woman she now is, but Marni can't let go of the past. The same holds true for her mom when Joanna's aunt, Ramona (SIGOURNEY WEAVER), shows up for the big weekend. A highly successful business woman, she's all lovey-dovey toward Gail, just like Joanna is to Marni, but Gail can't forget that Ramona turned from her best friend into her nemesis back in their high school days.
As they all take dance lessons with the flamboyant Georgia (KRISTIN CHENOWETH) who works in a dance studio owned by Tim (KYLE BORNHEIMER) who dated Joanna back in college, they must contend with their feelings about each other and their past, all while Marni tries to make an impression on her secret high school crush, Charlie (SEAN WING), who's also attending the wedding.