In this sequel to What Katy Did, Katy Carr has recovered from her long period of paralysis, and is sent, along with her sister Clover, to Hillsover boarding school. The girls fall into friendship with the mischievous Rose Red, and the three of them start a secret club and get into trouble with their teachers. During her time at Hillsover, Katy has a positive influence on the younger girls at the school, while they help her to regain some of her youthfulness, lost as a result of her illness.