Lars Lindstrom lives in a room adjacent to the garage behind the house he and his brother Gus inherited from their father. His pregnant sister-in-law Karin's persistent attempts to lure him into the house for a family meal are usually rebuffed, and on the rare occasions he accepts, their conversation is stilted and he seems eager to leave as soon as he can. The young man finds it difficult to interact with or relate to his family, co-workers, or fellow parishioners in the church he regularly attends.
One day Lars happily announces to Gus and Karin he has a visitor he met via the Internet, a wheelchair-bound missionary of Brazilian and Danish descent named Bianca. The two are startled to discover Bianca is in fact a lifelike doll Lars ordered from an adult website. Concerned about his mental health, they convince Lars to take Bianca to Dagmar, the family doctor who is also a psychologist. Dagmar diagnoses Bianca with low blood pressure and advises Lars he needs to bring her in for weekly treatments, during which she will attempt to analyze him and get to the root of his behavior. She urges Gus and Karin to assist with Lars' therapy by treating Bianca as if she were a real woman.
As time passes, Lars begins to introduce Bianca as his girlfriend to his co-workers and various townspeople. Aware of the situation, everyone reacts to the doll as if she were real, and Bianca soon finds herself involved in volunteer programs, getting a makeover from the local beautician, and working part-time as a model in a clothing store. Due to their acceptance of Bianca, Lars soon finds himself interacting more with people. At work, he takes notice of Margo, and when she reveals she has broken up with her boyfriend, Lars agrees to go bowling with her while Bianca attends a school board meeting. The two spend a pleasant evening, although Lars is quick to remind Margo he could never cheat on Bianca. She replies she would never expect that of him and tells him she hopes one day to find a man as faithful as he.
One morning, Lars discovers Bianca is unresponsive, and she's rushed to the hospital by ambulance. Her prognosis isn't good, and Lars announces Bianca would like to be brought home. News of her illness spreads through town, and everyone whose life has been touched by Bianca brings flowers or food to the Lindstrom home. Gus and Karin suggest Lars and Bianca join them for a visit to the lake. While the couple is hiking, Lars kisses Bianca for the first time, just before she dies.
Bianca is given a funeral all the townspeople attend. After Bianca is buried, Lars and Margo linger at the gravesite and, having come to terms with past traumas, ready to accept adult responsibilities, and filled with newfound self-confidence, he asks her if she would like to take a walk with him, an invitation she happily accepts.