While recovering from a long illness, Peter makes friends with Len, a disabled rabbit keeper. When Len gives him a rabbit he got from a circus, Peter soon finds out it possesses magical qualities and is named Thisbe.
Len encourages Peter to show Thisbe, sending her off to competitions all over the country, with increasing success. However, with the outbreak of myxomatosis, a disease that's fatal for rabbits, the shows stop.
When the disease has passed, the shows restart but Peter suffers a terrible loss when Thisbe is sent to compete again. However, it's not until he is taken to a circus at Christmas, that the mystery of Thisbe is explained.