Created by Brian Hayles, The Moon Stallion ran for six episodes in 1978 and followed a young girl named Diana (Sarah Sutton), who along with her archaeologist father and her brother visit friends in Berkshire near the site of the ancient Celtic horse cut into a chalky hillside. Though Diana is blind, she has the “sight” which connects her to a mysterious white stallion, to an ancient legend of Arthur as a Celtic chieftain, and to danger from others who seek paranormal power.
In Part 1, Professor Purwell’s investigations into the legend of King Arthur at Uffington cause him to stay at the home of Sir George Mortenhurze with his son Paul and his blind daughter Diana. En route, Diana senses the presence of a wild white horse, the mystic Moon Stallion, which Sir George blames for his wife’s death.
In the second episode the Moon Stallion appears for the third time at the prehistoric burial tomb of Wayland’s Smithy. Diana is overcome there and granted a vision of a dark rider astride the Moon Stallion, pointing. She feels this will help her father with his research. In Part 3, Sir George and his evil stablemaster Todman become increasingly concerned by Diana’s knowledge of the Moon Stallion which threatens their own plans to capture it. Paul and Estelle see Todman making a talisman to bring the horse under his power. At midnight, the Stallion carries Diana away into the darkness.
During Part 4, the Moon Stallion carries Diana to Wayland’s Smithy where she meets the ancient guardian of the Sacred Grove, The Green King, who asks Diana to activate his ancient powers of magic and grants her a vision of man’s future. Sir George tracks down the Moon Stallion, only to have it kill him.
In Part 5, Sir George’s attempted revenge on the Moon Stallion for his wife’s death has turned on himself, but Todman remains to try and fulfil his own and more dangerous and destructive ambition. Realising that Diana has a talisman and power from the ancients, he kidnaps her.
In the final episode, Diana faces extreme danger at the hands of the warlock Todman, but the ancient forces he conjures are gathering to oppose him … At the ancient burial mound, Todman challenges the awesome powers of the Green King to keep control of the Moon Stallion.