Matilda lives at Little Bagwood Farm with her mummy; daddy; and her older sister, Polly. For her seventh birthday, she gets a beautiful Welsh Mountain Pony, her name is Diva. All through the summer, they have so much fun together, going to shows and gymkhanas. Late in August, Diva has a foal, her foal is a unicorn. Because Diva is a Welsh pony, he is not a full unicorn. His sire (his father) is the Golden King, King of all the Unicorns, horses and ponies. The foal's name is Prince Argent, The Silver Prince. Time passes and Prince is maturing, and Matilda is now riding him. It is near to midsummer and very hot, so they go to the forest and when riding in the forest, a fairy princess, Princess Kessia, appears and gives a message from the Golden King. Matilda and Prince must go to the henge of stones on midsummer's day at midday and then the magic will begin and he will become a full unicorn. This is only the beginning of their adventures together.