In the quiet coastal town of Saint-Michel, a disturbing scene unfolds deep in the woods as an unknown figure digs beside a hidden shape.

Meanwhile in England, single mother Sarah Gleason sends her teenage daughter Katie on a school exchange trip to the south of France. Before Katie leaves, Sarah reminds her to stay in touch. The trip is supervised by teacher Neil Scott and Sarah's boyfriend Jason Bradley is driving the group to Saint-Michel.

Katie is assigned to stay with the well-respected Morvan family, whose daughter Emma greets her with an uneasy politeness. While Sarah spends a quiet weekend at home, Katie quickly becomes absorbed in to the social life of the exchange students. Parties, alcohol, and tensions within the group begin to surface.

Late one night, Sarah misses a call from her daughter. When Katie suddenly stops answering messages, Sarah's concern turns to alarm. The host family, the school, and the supervising teacher all insist that Katie is simply out with friends. But something about their explanations feels wrong.

Unable to shake the feeling that her daughter is in danger, Sarah flies to France. Once in Saint-Michel, she finds a town reluctant to answer questions. The police appear slow to act, the Morvans seem strangely calm, and students at the school are evasive.

As Sarah begins asking questions herself, she discovers Katie spent her last known night with a troubled local boy named Xavier and another unidentified girl. Surveillance footage soon confirms Katie was in town only hours before she vanished.

Then Sarah receives a message from Katie's phone - one that turns her worst fears into a terrifying possibility.
 

With the investigation gaining attention, tensions rise in Saint-Michel. Sarah confronts Lieutenant Virginie Taylor about the similarities between Katie's disappearance and the earlier case of Odile Lambert, a local girl who vanished years before.

Virginie reveals that new forensic evidence connects Xavier to Katie's belongings, while local authorities prepare a large search of the surrounding woods. Yet Captain Jerome Ricard appears reluctant to reopen Odile's case, warning Virginie against pursuing connections that could damage the town.

Refusing to step back, Sarah begins investigating on her own. Her search leads her to people who were connected to Odile years earlier, uncovering troubling accounts of how that case was handled - and how some leads may have been ignored.

Meanwhile, cracks begin to appear within the investigation itself. Virginie secretly reviews the old case file and discovers that several key details were never fully resolved. The revelations raise uncomfortable questions about people close to her.

As volunteers, students, and police comb the forest for evidence, Sarah notices strange relationships between several individuals involved in the search - connections that seem too coincidental to ignore.

Back at the school, tensions among the exchange students reach a breaking point. One student reveals disturbing messages sent to Katie shortly before she disappeared, pointing suspicion toward someone previously overlooked.

As new suspects emerge and personal secrets surface, Sarah uncovers another unsettling detail: on the night Katie vanished, she made a phone call to someone Sarah knows very well.

Moments later, a violent confrontation erupts that dramatically changes the course of the investigation.