Mary-Anna Clutterworth's mother and Sandra Sutton's mother are very good friends. Not once in ten years have they had the slightest argument. But Mary-Anna Clutterworth and Sandra Suttton absolutely hate each other. They are in the same class at school and, although they try their hardest to ignore one another completely, sometimes they are made to sit together. They trade deadly insults and don't let anyone see that they care one bit.

One day, to their horror, Mary-Anna is sent to stay at Sandra's house for the weekend. This means war!