Ruby wants a pet. She thinks it's very unfair that her older sister Jane is allowed a kitten for her birthday, especially when Jane refuses to let Ruby play with the kitten. So when she finds a very friendly-looking stone, she decides to adopt him as her pet. Jane thinks Ruby is being silly, but Ruby is pleased to discover that her new pet has some appealing characteristics - and she doesn't have to clean up any messes like Jane does! When the girls enter their pets in the school fete pet competition, there is a very surprising result.