When their relationship turns sour, a couple undergoes a medical procedure to have each other erased from their memories.
A man, Joel Barish, heartbroken that his girlfriend Clementine underwent a procedure to erase him from her memory, decides to do the same. However, as he watches his memories of her fade away, he realizes that he still loves her, and may be too late to correct his mistake.
A man awakes disheveled; impulsively, he skips work, heading instead to the shore. On this chilly February day, a woman in orange, hair dyed blue, chats him up: she's Clementine, he's Joel, shy and sad; by day's end, he likes her. The next night she takes him to the frozen Charles River. After, as he drops her off, she asks to sleep at his place, and she runs up to get her toothbrush. Strange things occur: their meeting was not entirely chance, they have a history neither remembers. Our seeing how the lacunae came to be and their discovery of the memory loss take the rest of the film.
Joel is stunned to discover that his girlfriend Clementine has had her memories of their tumultuous relationship erased. Out of desperation, he contracts the inventor of the process, Dr. Howard Mierzwaik, to have Clementine removed from his own memory. But as Joel's memories progressively disappear, he begins to rediscover their earlier passion. From deep within the recesses of his brain, Joel attempts to escape the procedure. As Dr. Mierzwiak and his crew chase him through the maze of his memories, it's clear that Joel just can't get her out of his head.
On a Valentine Day, Joel Barish feels the impulse of going to Montauk instead of working. After spending the cold day on the beach, he meets Clementine Kruczynski on the train station and they have a crush on each other. Joel and Clementine do not know that they were mates in the past. Joel has just erased Clementine from his memories when he found that Clementine did exactly the same, when their relationship ended. However, along his erasing process, Joel becomes astonished when he finds that he still loves Clementine and he does not want to lose her, fighting for keeping the memories of their moments together instead.
This is the story of a guy, Joel, who discovers that his long-time girlfriend, Clementine, has undergone a psychiatrist's experimental procedure in which all of her memory of Joel is removed, after the couple has tried for years to get their relationship working fluidly. Frustrated by the idea of still being in love with a woman who doesn't remember their time together, Joel agrees to undergo the procedure as well, to erase his memories of Clementine. The film, which takes place mostly within Joel's mind, follows his memories of Clementine backwards in time as each recent memory is replaced, and the procedure then goes on to the previous one, which is likewise seen, and then erased. Once the process starts, however, Joel realizes he doesn't really want to forget Clementine, so he starts smuggling her away into parts of his memory where she doesn't belong which alters other things about his memories as well...
- Joel Barish (Jim Carrey) is an emotionally withdrawn man and Clementine Kruczynski (Kate Winslet) is his girlfriend who is a dysfunctional free spirit. They are inexplicably attracted to each other despite their different personalities.
They do not realize it at the time, but they are former lovers now separated after two years together. After a nasty fight, Clementine has had her memories of their relationship erased from her mind. Upon learning this, Joel is devastated and goes to the doctor to have the same procedure done. However, while unconscious, Joel has second thoughts and decides he wants to keep his memories of Clementine.
Much of the film takes place in Joel's brain as he tries to find a way to preserve his memories of Clementine, and two Lacuna techies Patrick (Elijah Wood) and Stan (Mark Ruffalo) try to erase the memories. We watch their love and courtship go in reverse: The memories are slowly erased while Joel tries his best to resist the procedure and hide inside his mind.
In separate and related story arcs, the employees of Lacuna Corporation are revealed to be more than peripheral characters in scenes which further show the harm caused by the memory-altering procedure. Mary (Kirsten Dunst) has had an affair with the married Dr. Howard Mierzwiak, who heads the company (Tom Wilkinson). She agreed to have the affair erased from her memory when his wife discovered the relationship.
Lonely, socially inept Patrick becomes fixated on Clementine and uses Joel's personal mementos that he gave to Lacuna as part of the procedure in order to seduce her. These romantic entanglements turn out to have a critical effect on the main story line of the relationship between Joel and Clementine.
Once Mary learns of the affair she has had with Mierzwiak, she steals the company's records and sends them to all of its clients. Thus Joel and Clementine both get to listen to their initial tape recordings at Lacuna, and afterwards realize that even if everything in life isn't perfect, their relationship can still be worthwhile.