Months after a tragic accident, Sarah, a young pregnant woman, must spend Christmas Eve alone in her house before giving birth the next day. But in the middle of the night, a creepy visitor knocks at her door willing to do anything to get what they want, setting off a night of pure terror.

In Montreal, the unemployed fashion designer Sophie Malaterre is shown a 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 Bénédicte Serteaux and they change apartments. Sophie arrives in Paris on Saturday morning. 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 Bénédicte and she learns that a beheaded body was found in her room and all evidence of her life has been deleted.