One evening, just as she is getting ready to leave for home, Dr. Jenny Davin hears someone knocking on the surgery door. She decides to ignore them-it's late, the surgery is closed. But the next day she finds out that her unknown visitor was a young woman who died shortly afterwards, and not from natural causes. Stricken with guilt, Jenny takes it upon herself to investigate the circumstances around the girl's death-and puts herself in danger.

Increasingly, the Dardenne brothers have drafted their social realism in the form of suspense stories, in films like The Child, Lorna's Silence and Two Days, One Night. The Unknown Girl is essentially a mystery thriller filmed in a naturalistic style. But like all their work it is ultimately a philosophical drama, a morality tale about what ethical responsibility we have towards other people, and to seeking out truth. Rising French star Adèle Haenel doesn't just embody the intriguing doctor/detective dichotomy, but suggests a high-achieving, altruistic woman tormented by her own flaws and determined to rectify the world while she's at it.