After first crossing paths at a summer camp during their teenage years, Emma (Natalie Portman) and Adam (Ashton Kutcher) reconnect on several occasions in their young adulthood, yet struggle to maintain contact. Presently, Emma is a hospital resident in Los Angeles, while Adam works as a production assistant for a musical TV show. Complicating matters for Adam is the revelation that his father, a former television star played by Kevin Kline, is dating Adam's ex-girlfriend, Vanessa (Ophelia Lovibond).
After a night of heavy drinking following this shocking news, Adam drunkenly reaches out to various contacts in his phone, only to wake up on a sofa the next day, clad in just a towel. It turns out he had texted Emma and subsequently arrived at her apartment—where she lives with roommates Patrice (Greta Gerwig), Shira (Mindy Kaling), and Guy (Guy Branum). Upon arriving, he inadvertently stripped off all his clothes and passed out. With a boldness driven by impulse, Emma leads Adam to her bedroom to retrieve his missing pants, resulting in an unexpected one-night affair.
Their next encounter at Adam's residence leads to an agreement: a casual relationship devoid of emotional strings. Emma reassures Adam she won’t fall for him, and they establish ground rules to maintain a simple physical connection. Initially, things appear to be going smoothly; however, jealousy brews within Adam when he perceives attention from another hospital resident, Sam (Ben Lawson), directed at Emma. Adam attempts to express his feelings for her by gifting a personalized CD mix, but Emma dismisses this gesture, suggesting they date others for a while. After a two-week hiatus, Emma decides to reconnect with Adam, and they resume their purely physical relationship.
Fast forward to Adam's birthday in early February, a moment that sets off a series of emotional upheavals. At dinner with his father and Vanessa, Adam is taken aback when they announce their intention to have a baby. Emma, who accompanies him, defends Adam from criticism but encounters discomfort during their Valentine's Day date. When Adam professes his love, the situation spirals into an argument that brings their no-strings agreement to an abrupt halt.
Weeks pass, and Adam's career takes a leap forward when he secures a regular writing position on the show. Meanwhile, Emma finds herself sinking into despair over their breakup, especially leading up to her younger sister Katie's (Olivia Thirlby) wedding. Juggling familial responsibilities and her own heartache, Emma realizes she must confront her feelings for Adam. Encouraged by Katie, she reaches out but struggles to articulate her emotions during a phone call; Adam retorts that their relationship was never substantial.
Determined to reach out in person, Emma swiftly drives from the wedding venue in Santa Barbara to Adam’s home in Los Angeles. Just as she plans to approach him, she spots him arriving with Lucy (Lake Bell), which leads her to believe he’s moved on with someone new. Heartbroken, she retreats.
In the hospital, Adam receives a critical call from Vanessa about a family emergency involving his father, leading to an emotional reunion. With help from Shira, Emma learns about Adam’s father’s hospital admission and rushes there, rejoicing when she has the chance to see Adam once more. As the two meet, Emma bravely admits her lingering love for him, and the pair share an impassioned kiss, symbolizing a new beginning.
The next morning, in a moment of tenderness that marks their transformation, they arrive at Katie’s wedding just in time, their fingers entwined—signifying a romantic connection for the first time.
As the initial credits roll, glimpses of their friends' lives unfold—Adam's dad is seen dating Lucy, Adam's roommate is in a happy relationship, Vanessa grapples with her anxieties, and, ultimately, Emma and Adam are depicted in a serene moment, peacefully embracing in their newfound love.
