Pub. 1981. One of Lloyd Alexander's books in his classic Chronicles of Prydain series. Based on welsh legends. Tomboy Princess Eilonway must go the the Isle of Mona for training as a princess. But the evil echantress Achren thinks this is a good time to kidnap Eilonway and train her to use her magical powers. So The Assistant Pig-Keeper Taran, Prince Rhun, and Fflewddur Fflam the not so truthful bard must rescue her.
Taran and his companions accompany Princess Eilonwy to the island of Mona where the princess will begin her training in courtly etiquette. Once on the island they discover that their old nemesis Achren has returned to steal Eilonwy's magical heritage. The princess is kidnapped by a member of the royal court of Mona and imprisoned by he and Achren. Taran and the companions cast about the island in search of the princess and many new adventures along the way.