After years of a rocky relationship, Joel (Carrey) discovers that his long-time girlfriend, Clementine (Winslet), has undergone an experimental procedure in which all of her memories of Joel are removed. When Joel realizes what she's done, he's frustrated by being in love with a woman who doesn't remember him or the time they spent together, so he goes to the psychiatrist (Wilkinson) to have the same procedure. The procedure erases each memory at a time, with the most recent ones going first, and as this is happening, Joel realizes he doesn't really want to forget Clementine. He begins to hide her into parts of his memory where she doesn't belong, and in the process, alters his other memories.