In Montreal, the unemployed fashion designer Sophie Malaterre is summoned by Claire Maras to show her work to her boss. When Sophie arrives in the company, Clare apologizes and tells that her boss is on vacation and will return only two months later. Clare invites Sophie to have lunch with her and tells Sophie about the website switch.com, where it is possible to switch houses with a stranger for vacation. Sophie seeks an apartment in Paris nearby the Eiffel Tower that belongs to Benedicte Serteaux and they change apartments. Sophie arrives in Paris on Saturday morning and has a dream day riding a bicycle through the touristic area. However, on the next morning, policemen break in the apartment and arrest Sophie while she is having a bath. Detective Damien Forgeat interrogates Sophie believing that she is Benedicte and she learns that a beheaded body was found in her room...