“Roberta is the most embarrassing person in the universe and the most incapable mother of all time,” says 15-year-old Nana, who disapproves of her mother’s tendency for short and ill-fated romances. As a result, Nana has taken on the role of head of the household: she looks after her two younger siblings and earns their living by working as a lock keeper in a small town on the Rhine. When child services threatens to revoke Roberta’s custody, Roberta vows to change and remain celibate. Convinced that her mother won’t stay abstinent for long, Nana sets out to find a suitable man for Roberta – and a stepfather for herself and her siblings.