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 walk on the beach together. Danny tells her that this is the first time he's really connected with someone and they have sex. In the morning, Palmer asks Danny for his number and he tells her to check his pocket for a business card. However, 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, and Danny doesn't tell her the truth.



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, and that she cheated on him first. Palmer then insists on meeting Devlin, and Danny agrees. Danny returns to his office and asks Katherine to pose for him, saying he can alter her appearance with cosmetic surgery after she finishes so Palmer wouldn't recognize her when she would visit the office. 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, but takes the opportunity to make up embarrassing stories about Danny. When they are about to leave, Katherine gets a call from her kids. Hearing her conversation, Palmer assumes that her kids are Danny's as well, and Danny feels obliged to continue the charade by telling Palmer that they are his and Katherine's kids. Danny then privately meets with Katherine's kids, Maggie (Bailee Madison) and Michael (Griffin Gluck), to negotiate the terms of them posing as his kids. Katherine is furious that Danny wants to use her kids, 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, after getting into trouble with some people, has taken the disguise of "Dolph Lundgren" (not the actor), an Austrian sheep salesman and "Devlin's" lover. When arriving at a resort in Hawaii, Danny is forced to pay for the most expensive suites having not made a reservation.



During a luau, Katherine reaches breaking point, pulls Danny aside, and tells him that she will tell Palmer the truth and leave if he doesn't get things under control. At that moment, they 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 are spending time with Maggie and Michael, where Michael breaks down saying that his (real life) father won't make time for him, causing Palmer to get upset with Danny as she thinks he is their father. Palmer resolves to ask Katherine out for a day at the spa so Danny can spend time with the kids. The next day, 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. Katherine asks Eddie to take Palmer out away from the hotel so Danny can help her, so Eddie takes Palmer to a remote, rundown restaurant. Danny and Katherine go to a fancier restaurant with Devlin and Ian, and Devlin asks them 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 admiring the fact that he's never had to lie to her. Katherine and Devlin participate in a hula dancing contest, which ends in a tie, but the competitive Devlin wants a tiebreaker. So Danny and Ian join the two in a coconut rolling contest which Danny and Katherine win, Devlin showing herself to be a sore loser before storming off the stage.



When Danny and Katherine get back to her hotel room, they start to feel a connection and are about to kiss before being interrupted by her kids, so he heads back to his hotel room. Danny decides to go back to Katherine, but runs into Eddie and Palmer returning. Palmer tells him that Eddie mentioned Danny looking at engagement rings (Na Hoku Solitaire), suggesting that he was considering marrying her. Palmer says they should get married the following day, and Danny is surprised by her proposition, but ultimately agrees. Katherine, who was on her way up to see Danny, walks in on them and they tell her the news, leaving her surprised as well as she heads back to her hotel room. Later that night, Danny 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.



The next day, Palmer confronts Katherine regarding getting married to Danny, as she has noticed Danny's feelings for her. Katherine assures her it's fine and gives her blessing. Katherine then starts drinking at an outdoor bar where Devlin runs into her. Katherine admits that she made up being married to Danny to look impressive in front of her. Devlin confesses that she's divorcing Ian because he's gay and also that he didn't really invent the iPod; he got rich suing the Los Angeles Dodgers after getting hit by a foul ball. 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.