来自新泽西的汤姆（Joseph Gordon-Levitt约瑟夫•高登-莱维特 饰）是一个沉溺于英伦哀歌与《毕业生》情境的年轻人。他供职于一家贺卡公司，任务是撰写富有创意的祝辞。某次会议上，汤姆的老板把新助理介绍给大家，她是来自密歇根的魅力女孩莎莫（Zooey Deschanel 佐伊•丹斯切尔 饰）。莎莫自幼父母离异，因此对于感情的态度与众不同。汤姆和莎莫没有一见钟情，但却在一次酒吧K歌后彼此示好，成了非典型的恋人。而且这段办公室恋情迅速升温，爱火烧得谁都无法预料。最后，在一个餐馆里，莎莫对汤姆说了绝情的分手。深陷情网的汤姆，经受不住失恋的打击，郁郁寡欢，周围的伙伴们希望帮他走出阴影，然而，这并不是故事的全部，本片以汤姆的视角把时间重新组接，让观众在对比中体味500天恋爱的弦外之音……After it looks as if she's left his life for good this time, Tom Hansen reflects back on the just over one year that he knew Summer Finn. For Tom, it was love at first sight when she walked into the greeting card company where he worked, she the new administrative assistant. Soon, Tom knew that Summer was the woman with whom he wanted to spend the rest of his life. Although Summer did not believe in relationships or boyfriends - in her assertion, real life will always ultimately get in the way - Tom and Summer became more than just friends. Through the trials and tribulations of Tom and Summer's so-called relationship, Tom could always count on the advice of his two best friends, McKenzie and Paul. However, it is Tom's adolescent sister, Rachel, who is his voice of reason. After all is said and done, Tom is the one who ultimately has to make the choice to listen or not.