If you were given the opportunity to disappear and start your life again, would you take it?

Paris 1933. Four people's lives are dramatically torn apart by a single terrifying event. Two days before Christmas the express train to Strasbourg crashes into a local train in the winter darkness outside Paris. On board is Gilles Malroux, a man with a shady past and a strong reason to avoid the police. In the mayhem of the crash he is badly injured but to avoid capture by the police he swaps identity papers with one of the other victims of the impact. Gilles tries to flee in the dark but finds himself taken to the house of a woman he doesn't know but who calls him Davide. She nurses him. But is the bitter medicine in the spoon she puts to his lips healing him or harming him?

Camille Malroux is Gilles' sister. She works for the French Civil Service and is trying to climb the ladder of respectability after a childhood in poverty. When she is informed by police that her brother is seriously injured in hospital, she rushes to his bedside, only to discover it is not Gilles. It is a heavily bandaged stranger. He is unconscious and has her brother's identity papers in his locker. Only by digging to discover the true identity of the bandaged man in the hospital bed can she hope to trace Gilles.

But Gilles is sinking into further danger. He is drugged. A priest and a doctor hover over him, as if waiting for him to die, and constantly the woman who calls him Davide is at his side. What is it she wants from him?