Danny Maccabee (Adam Sandler) is a successful plastic surgeon in Los Angeles who feigns an unhappy marriage to get women, after having been heartbroken on his wedding day 20 years ago. The only woman aware of his schemes is his office manager Katherine Murphy (Jennifer Aniston), a divorced mother of two. At a party, Danny meets Palmer (Brooklyn Decker), a sixth grade math teacher, without his wedding ring on, and they have a connection together. The next morning, she ends up finding the ring, and she assumes he was hiding the fact he was married. She refuses to date him because her parents divorced due to adultery.
Danny goes to Palmer's school to try to woo Palmer back. Instead of telling her the truth, he tells her that he is getting divorced from a woman named Devlin, named after Devlin Adams, whom Katherine had mentioned was an old college sorority nemesis. Palmer then insists on meeting Devlin, and Danny agrees. Danny asks Katherine to pose for him, and they go shopping on Rodeo Drive to buy her clothes so she can look like a trophy wife.
At a hotel having drinks, Danny and Palmer are greeted by a made-over Katherine, who gives them her blessing. However, after hearing Katherine talking on the phone with her kids, Palmer assumes that her kids are Danny's as well, which Danny goes along with. Danny then privately meets with Katherine's kids, Maggie (Bailee Madison) and Michael (Griffin Gluck), to get them to play along. Initially Katherine is furious, but she reluctantly agrees.
Palmer meets the kids, with Maggie using a fake British accent. Michael blackmails Danny in front of Palmer to take them all to Hawaii. At the airport, they are surprised by Danny's cousin Eddie (Nick Swardson), who has taken the disguise of "Dolph Lundgren" (not the actor), an Austrian sheep salesman and "Devlin's" lover. At the resort in Hawaii, Danny and Katherine run into the real life Devlin Adams (Nicole Kidman) and her husband Ian Maxtone-Jones (Dave Matthews), who allegedly invented the iPod. Because of Katherine and Devlin's long time rivalry, Katherine introduces Danny as her husband.
Danny and Palmer spend time with Maggie and Michael, during which Michael breaks down. He says that his (real) father won't make time for him, causing Palmer to get upset. Palmer resolves to spend time with Katherine so Danny can spend time with the kids. Danny teaches Michael how to swim, and Katherine and Palmer look on in admiration at Danny winning the kids over.
Katherine runs into Devlin, who invites her and Danny out to dinner. Eddie agrees to take Palmer out in the meantime. At dinner, Devlin asks Danny and Katherine to tell each other what they admire most about each other. They end up saying honest things to each other, with Katherine admiring his sense of humor, and Danny liking the fact that he's never had to lie to her. Danny and Katherine start to feel a connection, but when Palmer and Eddie return from their dinner date, Palmer suggests that she and Danny get married. Danny and Katherine are both surprised by her proposition, but Danny ultimately agrees. Danny later calls Katherine regarding his confusion, but Katherine says that she will be taking a job in New York City she mentioned to him earlier to start fresh.
Palmer confronts Katherine regarding getting married to Danny, as she has noticed Danny's feelings for her, which Katherine dismisses. Katherine then runs into Devlin at a bar and admits that she made up being married to Danny to avoid embarrassment. Devlin confesses that she's divorcing Ian because he's gay and also that he didn't really invent the iPod. Katherine confides in Devlin saying she's in love with Danny even though they won't be together. Danny, however, shows up behind her, telling her that he didn't go through with marrying Palmer and that he's in love with Katherine and the two share a kiss.
Danny and Katherine continue their vacation without Palmer, who heads back to the mainland alone, meeting a professional tennis player (Andy Roddick Brooklyn Decker's real-life husband) on the plane ride back who shares her interests. Sometime later, Danny and Katherine get married.