Hugo Claus rewrote and directed Friday as the cinematic version of his original 1969 play of the same name. Just as in the play, the story begins with the theme of incest, as the father Georges (Frank Aendenboom) returns from serving his jail sentence for that crime. Unlike the earlier play, however, the film does not emphasize that aspect of the story. When Georges gets home he finds out that his wife Jeanne (Kitty Courbois) has had an illegitimate child by a younger man, Erik (Herbert Flack), and now both of them must somehow try to return to a normal life, given their only too obvious lapses in moral judgment. As the husband and wife try hard to accommodate each other's failings and start to get to know each other again, Erik comes back into the picture. Now the three of them must resolve the deep-seated conflicts that brought them to this emotionally-wrought juncture of love and betrayal.
Rémi is a man trapped in a deteriorating marriage. When his wife is unexpectedly killed in a car accident, Rémi is left with his stepdaughter, Marion, who chooses to stay with him rather than live with her birth father.
Frank is an expert professional safecracker, specialized in high-profile diamond heists. He plans to use his ill-gotten income to retire from crime and build a nice life for himself complete with a home, wife and kids.