Laurel and Audrey (Zoe Kazan) are identical twins. Although they look the same on the outside, their personalities are very different, with Audrey being popular, sophisticated and successful while Laurel is shy, childlike, awkward and still living at home with their widowed father (John Carroll Lynch) and his new fiancée, and helping him with his work of reproducing famous paintings. At their birthday party, Audrey decides to take Laurel to live with her, and in preparation to the move, Laurel gets a new haircut that makes her look like her sister. Returning from the hair salon, they get in a severe car crash together, and when Laurel wakes up in the hospital, she is informed that her sister has died. Suffering from post-traumatic amnesia, Laurel doesn’t remember who she is at first and due to her new haircut and the fact that the deceased’s body was burned beyond recognition following the accident, everybody assumes she’s actually Audrey. The morning of her sister’s funeral, Laurel remembers her actual identity but decides to keep everyone thinking that was Laurel the one who died in the crash, especially when she realizes nobody at her funeral has anything to say about her.
Laurel flies back to the city where Audrey used to live and work as a real estate agent. There, she meets her late sister’s tenant, Basel (Jake Johnson), who is confused about Audrey’s sudden change of personality, because Audrey was never nice to him before. While posing as her sister, she learns that Audrey had a married boyfriend, Charles (Ron Livingston), but broke up with him before the accident. Laurel continues to spend more time with Basel and Audrey’s best friend and coworker Claudia (Frankie Shaw), who grows suspicious due to Audrey’s change of behavior and sudden lack of skills at work.
Eventually, Laurel and Basel fall in love and begin a relationship. When she finally feels that she is adapting to her new life, Laurel accidentally introduces Charles as her ex-boyfriend to her boss Edith (Sabrina Lloyd), not knowing that Charles is actually Edith’s husband, and getting immediately fired as a result. Shortly after this, Basel proposes to Laurel saying that he has loved her since they first met, which to Laurel means he loves her as Audrey, not as herself. Unable to continue deceiving everyone, Laurel reveals the truth to Basel, but he is devastated by her deception and breaks up with her.
Laurel returns to her father’s home, who’s also shocked to hear what Laurel did, while at the same time being relieved that the daughter he felt closer to is still alive. They have another funeral for Audrey, and after talking to Claudia and receiving praises and encouragements from her father after showing him her original paintings, Laurel eventually comes to terms with her own insecurities about being the less worthy sister. She returns to the city as herself and looks for Basel who’s still upset but also still in love with her. In the end he forgives her, and they share a kiss and start making plans for the future.