Lars purchases a life-sized doll named Bianca from the internet. He introduces the doll to family and friends. His psychologist says that Lars is delusional, which why he behaves as if the doll is a real person. She also says that everyone should play along while she helps Lars in therapy. Everyone in the small town plays along and Lars and Bianca lead a full life.
Lars becomes interested in a girl name Margo at work. As he becomes more interested in Margo, Bianca becomes ill and eventually dies. Once Bianca dies Lars asks Margo if she’d like to take a walk, implying that he starts a relationship with the real girl Margo and no longer needed the Bianca delusion to cure his loneliness.