In Los Angeles in 2003, after an evening of playing poker with another couple, Debbie Dunn (Reese Witherspoon) and Peter Coleman (Ashton Kutcher) have sex and spend the night together in her home. Peter calls Debbie later and says that he is not looking to date anyone as he is unpredictable. Peter is a budding writer. Debbie wanted to be an editor, but ended up making practical choices after she has a kid.Twenty years later, Debbie and Peter are best friends. He has moved to New York City and become a successful businessman, while she still lives in Los Angeles and works as an accountant at her son Jack's (Wesley Kimmel) middle school. Debbie calls Peter on his birthday, and they discuss her plans to head to New York soon to complete an accounting program to help her get a better-paying job (she needs this job to pay for Jack medication which costs $1000 per month and is only covered by insurance for another 6 months). During her stay in New York, Debbie will be staying at Peter's apartment.Debbie's ex-husband's (Jimmy) actress girlfriend, Scarlet (Rachel Bloom), is to watch Jack for the week but flakes when she is offered a role in Vancouver for two weeks. Peter, who has just broken up with his girlfriend and is between jobs, offers to go to LA to take care of Jack. Jack is a teenager. Peter knows that Debbie is having a panic attack about leaving Jack back home for a week. He calls Debbie's style Saran Wrap parenting. Zen (Steve Zahn) is Debbie's gardener. Debbie is shown to be an overbearing parent to the extent that she tells Jack whom to hang out with at school. Peter has been with his current girlfriend Becca (Vella Lovell) for 6 months. She has never met Debbie, but is a bit concerned about how much time Peter spends with her on the phone. She wants to know if she is wasting her time. Peter hesitates and Becca walks out. Peter is a marketing consultant, whose contract has just ended, so he is in between jobs.In California, Peter learns the extent of Debbie's overprotective parenting and decides to help Jack loosen up a little. Peter learns that Jack plays hockey. He cant play basketball, as he is allergic to the gym, no baseball as he is allergic to grass. Debbie has told Jack that playing hockey is too dangerous. Jack is not allowed to watch TV while eating and never before homework. Debbie doesn't allow takeout's at home either. Peter learns that Zen is a wealthy man due to a tech buyout and just does Debbie's garden as a hobby. Peter gets sky-box tickets to a Los Angeles Kings game and encourages Jack to invite along two classmates (to help him make friends at school), but this goes awry when they ignore him.Meanwhile in New York, Debbie attends her accounting classes and meets Peter's ex-girlfriend, Minka (Zoë Chao) (who had come to meet Peter for a booty call, but met Debbie instead), who invites her out for drinks. At the bar, Minka helps her catch the attention of book publisher Theo Martin (Jesse Williams) from Duncan Press. Debbie tells Theo that she has read every Duncan Press book ever published. Minka also informs Debbie that Peter has written a novel. This comes as a shock to Debbie as Peter never told her that he wrote a novel. Debbie reads the novel in less than a day and loves it. After reading the manuscript, Debbie pretends to be an editor as she tries to convince Theo to give it a chance. Theo and Debbie are both divorced and have 13 yr old boys each. Theo loves the book and wants to speak with the author.Peter grows closer to Jack and convinces the hockey coach to let him try out for the team. Peter befriends Zen and finds out that he is also Debbie's part time lover. Meanwhile, Debbie goes out on a date with Theo, which ends with them having hooked up and spent the night together. Debbie accidentally sets off the apartment's remote camera, leading to Peter witnessing them. Disturbed, he goes to a bar and meets an old girlfriend but cannot bring himself to sleep with her. He realizes that he is in love with Debbie.On Debbie's last day in New York, she passes her exam and unintentionally discovers Peter's hidden mementos of her. When Debbie meets with Theo, he informs her that he has gotten her an interview with a major publisher. When he expresses a desire to continue dating her, she confesses that she is in love with someone else.In Los Angeles, Jack's hockey tryout goes badly, and he ends up injured. Peter calls Debbie, and she is enraged that he endangered her son even though Jack appears to be okay. Jack is happy to be on the hockey team and tells Debbie not to yell at Peter at any cost. Jack loved his week with Peter. She rushes to leave and get back home to Jack and tells Peter to be gone by the time she arrives. Peter and Debbie come face-to-face at LAX. After a heated argument, Peter admits that he is in love with Debbie, and they kiss. Six months later, Peter has become a published author and moved in with Debbie. She is an editor at an indie publishing house, and Jack is playing on the hockey team.