Sophie Malaterre, an unemployed Canadian graphic designer, spontaneously accepts a chance of a holiday abroad: from an acquaintance, Claire Marras, she learns of a website called "Switch", through which she can temporarily swap her home for someone else’s.

Back at the apartment, Sophie prepares a meal with food from the refrigerator, which she eats in the garden within sight of the Eiffel Tower.

She takes a shower to refresh herself, but is alarmed when a police task force storm into the apartment and proceed to search it.

In the locked room, a headless corpse is found; the man is Thomas Huygens, the boyfriend of Benedicte Serteaux.

At the police station, Sophie tries to convince the investigators that she is not Serteaux, but any evidence that would prove her true identity seems to have been destroyed overnight.

Sophie is taken for a psychiatric assessment, as Benedicte’s records show that she has a history of mental problems, suicide attempts and criminal behaviour.

She is about to be temporarily committed to a psychiatric ward, while further investigations are carried out in Montreal, but in despair Sophie begs Forgeat to take her to a dentist, believing this will reveal that work done on her teeth is not of French origin.

On the run, a desperate Sophie hijacks a car and forces the driver, a young Japanese woman, to hand over her credit card and PIN.

Sophie takes the Metro to another area, where she finds a small shop selling a variety of items, including clothes.

She tells the taxi driver to take her to Sophie’s address, stopping only to collect a package from a delivery office.

When Marianne Malaterre arrives at the darkened house Sophie has a change of heart and pleads with her mother to call the police instead of entering on her own.

After a lengthy chase through gardens and houses, Sophie reaches a busy road, steals a man’s motorbike, and rides off.

By this time, Montreal police have also gone to the house of Claire Marras, and find her lying dead, with her throat cut, in a blood filled bath.

Bénédicte tells her that she had the worst childhood imaginable, with a mother who hated her, and when she found out who her biological father’s other children were, she decided to punish them for having been happy when she was not.

Bénédicte had cosmetic surgery to look more like Sophie, and she employed Claire Marras, who was a computer expert, to create the Switch website.