The movie opens with Carly Whitten (Cameron Diaz) and Mark King (Nikolaj Coster-Waldau) after a blind date that quickly turns into a one-night affair. Fast forward eight weeks, they are happily dating, and Carly, a driven single career woman, shares her newfound romance with her friend and secretary Lydia (Nicki Minaj), who points out that Carly hasn't been romantically involved in a while. However, unbeknownst to Carly, Mark is actually married to his chatty and neurotic wife, Kate (Leslie Mann).
When Mark concocts a story about plumbing issues as a reason to leave town for a few days, Carly becomes frustrated and their relationship faces a bump. After arguing, Mark drops her off to meet her dad, Frank (Don Johnson). Following her father’s encouragement, Carly decides to surprise Mark, dressing up as a sexy plumber for the occasion. Unfortunately, she is met by Kate, who introduces herself as Mark's wife, leaving Carly shocked and stumbling backward, resulting in a mishap with a large urn.
The next morning, Carly storms into work, angry and hurt, tearing apart the flowers Mark sent her. She confides in Lydia about Mark's marital status, but Lydia sees potential excitement in this twist. The plot thickens when a distraught Kate approaches Carly, having discovered the truth, and despite their initial animosity, the two women slowly become unlikely friends. In a fit of rage, Kate even goes so far as to vandalize Mark's office using a golf club.
Mark, trying to maintain his charade, takes Kate out for a romantic evening, but she overhears a call from another woman and pretends to feel ill to avoid intimacy. Amidst mounting tension, Kate confides in her brother Phil (Taylor Kinney) about her suspicions, leading to a confrontation with Carly where they realize they are both entangled with the same deceitful man.
Things take a turn as both women, alongside a stunning new love interest of Mark, Amber (Kate Upton), find themselves in Miami, following him to uncover the truth. Shockingly, they discover Mark's new partner is far younger than both, reigniting insecurities and leading to an explosive confrontation on the beach. After revealing his tricks to Amber, the trio builds a bond over their shared betrayal, even starting to plot revenge against Mark.
As they devise a plan, Kate decides to extract her own sense of justice by messing with Mark's products, and Carly escalates things by slipping laxatives into his drinks during their dates. The revenge escalates with hilarious, sometimes chaotic situations, leading to unintended romantic feelings, complicating their dynamic.
In a climactic showdown, they confront Mark at Carly's law firm, presenting him with the consequences of his actions. The scene culminates in Kate demanding a divorce, while Mark's web of deceit unravels before him, leaving him with nothing as the three women take a stand against him. Mark’s defeat is depicted through humorous chaos, culminating in a physical mishap as he realizes the full brunt of his betrayal.
The film concludes with a heartwarming reunion among the women—celebrating their new chapter, with Kate thriving in her career, Carly in a new relationship with Phil, and Amber embarking on globetrotting adventures with Frank, albeit with a playful twist. The final message emphasizes their newfound friendship and strength, setting the stage for their bright futures.
