Tom Hansen is a trained architect working as a greeting card writer in Los Angeles. When he meets Summer Finn, his boss’s new assistant, he’s instantly drawn to her. They bond over their shared music tastes, and during a work karaoke night, they discuss love: Tom believes in it, but Summer is skeptical. Tom’s friend McKenzie drunkenly reveals Tom’s crush, which Tom downplays as friendship, and Summer agrees. A few days later, however, Summer surprises Tom with a kiss in the office, leading to a casual relationship.
As their relationship develops over several months, Tom’s friends and his younger half-sister Rachel encourage him to define his connection with Summer. However, Summer avoids labeling their relationship, emphasizing that happiness matters more than titles. Despite their close bond, conflicts begin to surface. After Tom gets into a fight with a man who hits on Summer at a bar, they argue but eventually reconcile. Summer concedes that Tom deserves certainty but insists that no one can guarantee unchanging feelings.
Their relationship grows strained as Summer becomes distant. During a movie night, she weeps at the ending of The Graduate, which Tom interprets as a troubling sign. Soon after, she breaks up with him in a diner, leaving him devastated. Summer quits her job, and Tom’s boss moves him to the consolations department due to his depression. He tries dating someone new, Alison, but spends the entire date talking about Summer, prompting Alison to leave.
Months later, Tom sees Summer at a co-worker’s wedding. They spend the day together, dancing and reminiscing, and Summer catches the bridal bouquet. She later invites Tom to a party at her apartment, where he arrives hopeful for a reconciliation. Instead, he notices an engagement ring on her finger, which leaves him crushed. Tom spirals into depression, only venturing out for junk food and alcohol. After an emotional outburst at work, he quits his job. His sister Rachel helps him recognize that he has been idealizing his time with Summer and overlooking signs of their incompatibility.
Inspired, Tom rededicates himself to architecture, a passion Summer had encouraged. He creates a portfolio and begins interviewing for architecture jobs. One day, Summer meets Tom at his favorite spot in the city. She tells him that she got married because she felt certain about her new husband in a way she never felt with Tom. Although he initially doubted true love after their breakup, she assures him he was right about love—just wrong about it being with her. They part on good terms, with Tom wishing her happiness.
A short time later, Tom meets another woman named Autumn while interviewing for a new job. She shares his favorite spot in the city, and they have an instant connection. As they enter the interview, Tom invites her for coffee. She initially declines but changes her mind, hinting at a new beginning for Tom.
