The film opens with Leonard, portrayed by Joaquin Phoenix, walking across a footbridge over the Sheepshead Bay creek in Brooklyn while carrying dry cleaning. In a moment of despair, he drops the clothes and attempts to end his life by jumping into the water. Just as he is about to give up, he changes his mind and surfaces to be rescued by a passerby. Upon returning home to his parents' apartment, it becomes clear that Leonard is struggling with deep emotional issues, and when his mother sees him drenched, it is evident that this isn’t his first attempt at suicide.
His parents soon inform him that they have invited a potential business partner and his family over for dinner. To his surprise, Leonard finds himself set up with their daughter, Sandra, played by Vinessa Shaw. Over the course of the evening, he shares with Sandra that he was once engaged but had to end the relationship after genetic counseling revealed serious concerns regarding having healthy children.
Not long after, Leonard crosses paths with his new neighbor, Michelle, played by Gwyneth Paltrow, in the hall of their apartment building. He is instantly smitten with her, and they embark on a whirlwind romance, spending time together and mingling with her friends. However, he soon discovers that Michelle is involved with Ronald, a married partner at her law firm. After an awkward dinner with Michelle and Ronald at a fancy restaurant, Leonard returns home feeling troubled. Unexpectedly, Sandra surprises him at his apartment, leading to a brief intimate encounter between them.
The next day, Leonard decides to sever ties with Michelle and pursue a deeper relationship with Sandra. As time passes, he is asked to take photographs at Sandra's brother's Bar Mitzvah, but his life takes another twist when he receives an upset call from Michelle, revealing that she is in the hospital due to a miscarriage—a surprise to her as she didn’t even know she was pregnant. After he takes her home, Michelle’s partner Ronald shows up, prompting Leonard to hide and listen as Ronald makes excuses for his absence. In a moment of vulnerability, Michelle asks for Leonard’s company, requesting that he stay by her side until she drifts off to sleep.
Two weeks later, Michelle invites Leonard to meet her on the rooftop, where she shares that she has ended her relationship with Ronald and is planning to move to San Francisco. In a moment fueled by love, Leonard begs her not to go, and they share an intimate moment on the rooftop. He promises to join her the following day, excitedly buying two tickets and an engagement ring as he prepares for their new life together.
However, Leonard's world takes another turn when he learns from Sandra's father that he is being offered a partnership in Sandra's family business, under the assumption that a marriage proposal is imminent. On New Year's Eve, amidst his family's celebrations, Leonard sneaks outside to meet Michelle on the courtyard. There, she heartbreakingly informs him that Ronald has left his wife and will be marrying her instead. Deeply crushed, Leonard wanders to the beach with thoughts of another suicide, but as he steps into the ocean, he finds and picks up a glove that Sandra had gifted him. Returning to the party, he sees Sandra and decides to propose, giving her the ring, marking an emotional climax in his turbulent journey.
