Marni, a successful PR executive, is excited to return home for her brother Will’s wedding. However, her excitement quickly turns to horror when she discovers his fiancée is Joanna, the girl who bullied her relentlessly in high school. Determined to protect her brother, Marni sets out to expose Joanna's true nature and prevent the marriage, even as Joanna appears to have turned over a new leaf and won over the rest of Marni’s family.

As the wedding preparations move forward, tension escalates not only between Marni and Joanna but also between their mothers, Gail and Ramona, who share an unresolved rivalry from their own high school days. Old wounds are reopened, secrets come to light, and both past and present grievances threaten to derail the upcoming nuptials. With a blend of humor and heartfelt moments, the families must navigate their complicated histories and find a way to coexist for the sake of their loved ones.