The Promise.

What's the worst that can happen to a police officer? Definitely an unresolved investigation. This is what happens on Boxing Day 1999. Charlotte Meyer, an 11-year-old girl, disappears without a trace. Captain Pierre Castaing, in charge of the investigation, fails to find her. Where did she go? The mystery remains intact ... A few hundred kilometers away, a young investigator finds herself confronted with a similar disappearance ...