Sophie Malaterre, a recently unemployed Canadian graphic designer, stumbles into a chance for a holiday abroad through a swap service called Switch. She arranges a temporary exchange of homes with a Paris apartment owned by a woman named Bénédicte Serteaux and, after exchanging keys by mail, flies to Paris ready to enjoy a new city and a new routine. On arrival, Sophie is thrilled with the stylish flat and the chance to explore, though one room remains locked and without a key, a mystery that whispers through the first taste of her stay. The city welcomes her with the glow of the Eiffel Tower at dusk, and she spends a day wandering, snapping photos, and messaging Claire Marras, the acquaintance who told her about the switch. A short encounter with a charming young man named Kourosh leaves her with his number, hinting at a budding connection she might pursue while away.
Back at the apartment, Sophie makes a simple dinner from the food in the fridge and settles into a moment of quiet in the garden with a view of Paris that feels almost cinematic. Yet the next morning’s routine is shattered by a violent intrusion: a police task force storms the place. In a locked room, a headless corpse is found—Thomas Huygens, the boyfriend of Bénédicte Serteaux. The investigators assume Sophie is actually Bénédicte, and they arrest her in a gravity that does not blink. The arrest launches a tense inquiry where Sophie maintains she is not Serteaux, but the evidence seems to have vanished overnight, including traces of Switch and Sophie’s Paris flight. She speculates that she was drugged, but the police aren’t convinced.
At the station, clues proliferate in unsettling ways. A passport bearing Sophie’s photo in Bénédicte’s name turns up, the internet footprint of Switch is erased, and neighbors identify Sophie’s image as Bénédicte’s. Sophie’s Montreal ties loom large as she irons out memories of a childhood in France and her own origins become a puzzle the investigators want to solve. The lead detective, Forgeat, questions why a person from Montreal would lack an accent, prompting Sophie to explain that she lived in France until age twelve. With her mental health history flagged in Bénédicte’s records, Sophie faces the prospect of psychiatric commitment even as she asks for a blood-type test to compare hers with Bénédicte’s. To everyone’s surprise, the rare blood types match, deepening the conviction that Sophie is indeed Bénédicte.
Desperation accelerates the action: a dentist’s visit becomes a critical scene where Sophie, handcuffed, uses the moment to seize control of the situation. She forces Forgeat to unfasten her cuffs, then grabs Bénédicte’s file and a gun, and escapes. On the run, she hijacks a car and forces the driver—an Irish or Japanese tourist?—to reveal her credit card details, explaining that she is being compelled by the police. She travels through Paris, buying clothes and a new phone at a small shop where the owner senses danger but offers quiet support. The pursuit continues across the city as Sophie disappears into the urban maze.
Meanwhile, back in Montreal, a woman arriving from Paris—wearing a headscarf and sunglasses—goes to Sophie’s address, stops by a delivery office to pick up a package, and becomes a focal point for investigators who later question her, convinced she is Sophie. The plot threads begin to converge as Forgeat engages with Alice Serteaux, Bénédicte’s mother and a renowned sculptor whose DNA-themed artworks foreshadow the story’s true hinge. Alice identifies Sophie in a photo, but the real significance lies in a hidden connection between the two families. Forgeat steals a sample of hair from Alice’s hairbrush, a quiet move that will prove pivotal later.
Sophie, now holed up in a hotel, keeps her lines of communication open with her mother, Marianne, who is back in Montreal. Sophie asks Marianne to come to her house and uncover something that could prove her identity, and the two stay in touch through calls and messages as Marianne makes the journey. When Marianne arrives at Sophie’s house in Montreal, she finds the lights out and a chilling discovery: Thomas Huygens’s severed head on a pillow in Sophie’s room, surrounded by blood and symbolic graffiti. Marianne’s frantic attempt to flee ends in tragedy as a woman dressed in black—presumably Bénédicte—attacks and mortally wounds her, setting the scene for a house that becomes a crime tableau and a fire threat.
The next day, a hotel manager recognizes Sophie from TV coverage and alerts the Paris police. Forgeat returns to the chase with a fellow officer, and Sophie proves herself to be a formidable runner, weaving through gardens and streets until she reaches a crowded avenue and borrows a motorbike from a stranger to disappear into the city’s flow once more. The investigation expands as back in Montreal, Claire Marras—who helped to create and later erase Switch’s footprint—appears in the capital, with investigators discovering Claire’s death soon after, her throat cut and a sizable cash transfer traced to the sequence of events. The detectives piece together a startling lineage: Sophie and Thomas are revealed as half-siblings through DNA analysis, a fact that casts their estranged family histories in a new light.
The film’s central revelation lies in the donor’s lineage. Forgeat learns that Sophie’s father, who lived in Paris, once sold his sperm to support his family, unknowingly producing both Thomas and Bénédicte as biological half-siblings. Bénédicte, adopting a false identity and leveraging her position at a laboratory, discovers the truth about her parentage and orchestrates a retaliatory plan that targets Sophie and others connected to their shared origin. Claire’s involvement as a technical architect behind the Switch scheme—and the subsequent erasure of digital traces—becomes a crucial thread in understanding how the illusion of identity was manufactured.
With the net closing in, Sophie seeks refuge with Kourosh, the Paris contact who once offered a friendly shoulder. He initially appears sympathetic, but a closer listen reveals he is entangled with Bénédicte’s schemes. Sophie escapes his apartment, yet he pursues her to a fatal balcony fall that ends his life in the street—an abrupt reminder of how perilous the web of deception has become.
Forgeat’s investigation finally connects the last pieces: Sophie’s parents’ past in Paris and the donor’s secret history illuminate the motive behind Bénédicte’s alarming violence. Sophie returns to Bénédicte’s flat in search of clues, only to be confronted by the now-dangerous rival. A struggle ensues, and she finds herself captured again, this time at a laboratory where Bénédicte’s plan draws to its violent apex. Bénédicte narrates a lifelike tale of a childhood ruled by hatred and a desire to punish those who found happiness she never had; she had undergone cosmetic surgery to resemble Sophie and had recruited Claire Marras to shape the Switch website and its digital footprints.
As the climax unfolds, Forgeat and his squad burst in, shooting Bénédicte dead and delivering Sophie from immediate danger. In the aftermath, Forgeat offers quiet reassurance, acknowledging that the truth has come to light and that Sophie can begin to heal from the ordeal. The emotional toll remains, but the immediate threat to her safety has receded, and the detective’s words anchor a sense of eventual safety and resolution.
What began as a spontaneous holiday turned into a labyrinth of identity, secrecy, and interwoven family histories. Sophie’s accidental entanglement with Bénédicte’s pursuit exposes a web of deceit built on stolen identities and mistaken perceptions of who belongs to whom. In the end, the truth—though brutal and unsettling—brings a kind of order: Sophie is spared from a complete collapse of her own sense of self, and a seasoned investigator’s determination helps untangle a network of lies that had threatened to consume her.
