Emma comes to her grandmother Dolly's for the summer holidays and learns to her horror that a dastardly neighbor – known by Emma and the local children as "the Alligator" – is planning to send his late uncle's horse Mississippi to the knacker's yard. Emma manages with the help of her grandmother and the local vet to buy Mississippi from the "Alligator". But then he is suddenly interested in reversing the sale when it turns out that the horse clearly plays an important role in the late uncle's will...