Jenny makes a friend on the train - Katie is a new girl too, and both girls are travelling to their new boarding school: Lilybrook Hall. But the journey doesn't go smoothly; into their carriage step two arrogant girls who punch a hole in Jenny's straw boater hat. To make matters worse, the two bullies are both prefects at Lilybrook, and are out to cause trouble for the two new girls. Having a sense of 'schoolgirl honour', Jenny fails to provide an explanation about the state of her hat, and gets the slipper from her housemistress, Miss Baxter. When Katie learns what happened, she goes storming off to tell Miss Baxter the truth but isn't believed - and she ends up getting caned on her bare bottom.

The two girls settle down and begin to enjoy school life (apart from the endless whackings with ruler, slipper and cane!), but they are constantly picked on by the prefects Miranda and Isobel, resulting in very sore bottoms. Although they confide in the head girl, she can do little about the bullies without proper evidence. Will justice prevail? Will the two bullies get their comeuppance? Or will Jenny, Katie and countless others continue to be punished without good reason...?