"Roberta is the most embarrassing character in the universe and the most incompetent mother of all time," says 15-year-old Nana, who condemns her mother's preference for short, unhappy flings and has therefore taken on her role in the house herself: she looks after her two younger siblings and earns a living as a lock keeper in the small town on the Rhine. When the youth welfare office threatens to take custody of the children away from Roberta, she swears to reform and abstain. Nana, who is convinced that her mother will not be able to remain abstinent for long, sets out to find a suitable husband for Roberta and a stepfather for herself and her siblings.