Rhinegold (1978)

A mature, rich and bored woman called Elisabeth is taking a ride with the "Rheingold", a first-class high-speed train of the seventies along the river Rhine. In the train she is meeting her old school mate and lover who is working as a waiter and falls in love with him again. Her husband, a busy politician, realizes what's going on and tries to catch the train to face his wife and her lover in a fatal showdown.