Christine (Doris Kunstmann) lives a comfortable, sheltered life in a relationship with the older, established Jochen (Bernhard Wicki). Her world shifts when she crosses paths with a young man named Stefan (Ulli Lommel). As they grow closer, it is revealed that Stefan and Christine are biological siblings who were separated as children following their parents' divorce and grew up completely apart. Upon reuniting as adults, their intense emotional bond quickly crosses conventional social and familial boundaries, evolving into an explicit romantic and sexual affair. This taboo relationship shatters Christine's conventional life with Jochen as they navigate the consequences of their reunited-sibling dynamic.