Joel Barish, a reserved and soft-spoken man, encounters the free-spirited and impulsive Clementine Kruczynski on a train trip to Montauk. Despite their seemingly disparate personalities, they form an unlikely connection, unaware that they are actually former lovers with a tumultuous past. Their previous relationship ended when Clementine, in a moment of frustration, sought the services of Lacuna, Inc., a company that specializes in erasing painful memories. She has had all memories of her relationship with Joel wiped from her mind.

Distraught upon discovering Clementine's memory erasure and unable to cope with the heartbreak, Joel decides to undergo the same procedure to remove his memories of her. During the process, as he relives each memory that is being erased, Joel experiences a change of heart and starts to remember the reasons he fell in love with Clementine in the first place. In a desperate attempt to preserve his memories, Joel subconsciously tries to outmaneuver the erasure by hiding Clementine in unrelated, deep-seated memories. As he endeavors to hold onto the moments they shared, the procedure's side effects begin to weave a tapestry of fragmented recollections and imaginings, making it increasingly difficult for Joel to distinguish between what was real and what was not.