Eleven-year-old Jess is distraught that she has to leave her beloved Exmoor when her widowed mother, Pam, takes a nursing job in Surrey. Her one consolation is she can take her pony, Marmalade, as her mother's employer, Mrs Carey, loves all equines. At her first Pony Club Rally, Jess is teased by smartly mounted children and resolves to have no more to do with them. She discovers that Mrs Carey's retired horse, cared for by Sam, a very elderly groom, is poorly and, when he is rushed into hospital, she and Pam take over as carers.

The vet, now regularly involved, has a twin son and daughter, who are pony-mad and become Jess's close friends. With their support Jess decides to learn more about dressage and show jumping and gradually life improves. Suddenly, things change; there is a horse attacker in the neighbourhood. Keeping their ponies safe is the most important job now and they are not convinced the police are doing enough. They send a letter to the local newspaper anonymously, and hear of no more attacks so concentrate more on Marmalade's schooling.

One afternoon, Jess is riding on a local estate, enjoying jumping. Suddenly, she sees a young man nearby, sharpening a large knife and close are a mare and foal. She realises it is the attacker and just manages to gallop off after he's attempted to grab the reins. She cannot return the way she's come so heads for another exit which is tricky - a five-bar gate, padlocked. Desperate, she manages to get small Marmalade to jump it and they follow a track that leads to a cottage. Here she gets wonderful help as the owners call the police who arrive quickly. The mare and foal are saved but the attacker isn't caught. Within twenty-four hours the event is in many newspapers. Soon the attacker is found - dead. He tripped and fell on his knife as he ran away.

Jess is regarded as a heroine and the new estate owner changes his mind about closing bridle-ways and is quickly in contact. The Pony Club members are delighted, and attitudes change towards Jess's Native pony. She wins the Junior class in the One Day Event and soon afterwards takes part in the Major County Show, winning Best Exmoor Pony. Astonishingly, Sonata is there, ridden by Pam - a secret kept from Jess.

Suddenly, an announcement says an Exmoor pony has just entered the tent where refreshments are being served. Clearly, Marmalade is enjoying a tasty reward!