One Night... a Train(1968)

Original title: Un soir, un train

The Belgian linguistics professor Matthias is going through a difficult period in relations with his girlfriend Anne. She is French, he is Belgian, and, oddly enough for an enlightened Europe and a doubly enlightened university environment, this small difference is a shadow on the couple’s personal life. One day, during a train ride, Anne disappears and Mathias goes looking for her in an unknown city.