Nicole Wagner finds out by chance that her son cannot be the son she once fathered with the scaffolder Grille. Nine years ago there was a mix-up with an infant named Sebastian, the son of the academic couple Callenberg, who live at the other end of Freiburg in very different circumstances to Nicole and Grille in their middle-class environment. Grille is inquisitive about the unknown son, unlike Nicole, who is very upset, as are Sven and Britta Callenberg. But what can be done? The children are anchored in their families, they are loved and nobody wants to make them unhappy. The parents reserve the right to leave everything as it is. But their thoughts about their biological son do not subside...