On January 8, Tom Hansen, portrayed by Joseph Gordon-Levitt, encounters Summer Finn, played by Zooey Deschanel, the new assistant to his boss. Although Tom is trained as an architect, he finds himself working as a writer at a greeting card company located in Los Angeles. Their connection reveals itself as they bond over shared musical tastes during a karaoke night, where their differing beliefs about love become apparent—Tom is a romantic, while Summer remains skeptical.
In a drunken moment, Tom's co-worker McKenzie inadvertently discloses Tom's feelings for Summer, which Tom brushes off as mere friendship, a sentiment Summer echoes. However, after a few days, Summer unexpectedly kisses Tom in the office. As the months pass, their relationship deepens. Tom introduces Summer to his favorite spot in the city: a park bench that offers a view of buildings he adores, though they are partially overshadowed by parking lots.
However, as their romance evolves, both Tom's friends and his young half-sister, Rachel, voiced by Chloë Grace Moretz, encourage him to seek clarity in their relationship. Summer, however, deflects, maintaining that happiness is what matters most to them. A night out leads to a heated argument when Tom confronts a man hitting on Summer at a bar. Although they reconcile, Summer acknowledges his desire for certainty is unrealistic.
On day 290, while spending time at a cafe, Tom longs to return to Summer's place, but she suggests watching The Graduate, which unexpectedly reduces her to tears at the end—a moment that surprises Tom, who had always viewed it as a romantic fairy tale. During a trip to a record store, Summer seems preoccupied, signaling a shift in her feelings. Their farewell kiss hints at a deeper disconnect, culminating in Summer breaking up with Tom while they wait for their food, sending him spiraling into depression.
After Summer resigns from the greeting card company, Tom’s melancholic state leads his boss to transfer him to the consolation department. In a misguided attempt to move on, Tom goes on a blind date with Alison, but he spends the night lamenting over Summer, frustrating Alison, who ultimately sides with Summer.
Several months later, Tom attends the wedding of a co-worker, attempting to dodge Summer but failing when she approaches him for coffee. They share a pleasant time at the wedding, dance together, and Summer even catches the bouquet. When she invites him to a party at her apartment, Tom hopes to reignite their romance but is devastated to notice her engagement ring during the night, prompting him to leave in tears.
Tom withdraws into deeper despair, only facing the world to drown his sorrows in alcohol and fast food. A few days later, after a hangover, he returns to work and, during an emotional breakdown, quits his job. Rachel tries to console him, stating that Summer was never meant to be “the one,” and his current bleak outlook stems from an overly nostalgic perspective of their relationship.
One day, however, Tom finds a renewed sense of purpose. He channels his energy back into architecture, the very field where Summer had pushed him to excel. He creates a list of architectural firms he aspires to join, curates a portfolio, and begins attending interviews. On day 488, at his beloved spot in the city, Summer unexpectedly awaits him. Their conversation reveals her marriage, which she explains stemmed from certainty—a contrast to her feelings for Tom. She reassures him that he was correct about true love, but it simply wasn't meant to be with her. Their exchange ends on a bittersweet note as she expresses gladness for his progress, and he genuinely wishes her happiness as she walks away.
Twelve days later, on Wednesday, May 23, during a job interview, Tom meets a girl applying for the same position. Their shared favorite spot and mutual disdain for the parking lots ignite a connection. Though she initially declines his invite for coffee, she quickly reconsidered, marking the beginning of a new chapter for Tom as he encounters Autumn.
