The lifeless body of the owner, Martha Balke, is found in a country house. For Derrick the case seems simple enough: the victim's husband, Alfred, inherits a great fortune with Martha's death and the man now also has the possibility of living with Roswitha, his young lover. Meanwhile, Marta's twin sister Johanna returns to Munich from the United States. When Derrick meets her he has an idea that could be helpful in framing the killer.