The Book of Three is the first novel in the five-novel series, Prydain Chronicles.
Following in the tradition of J. R. R. Tolkien and C. S. Lewis, Alexander creates modern fantasy out of the ancient Welsh myths of the Mabinogion, which date from the early Middle Ages, and the Arthurian traditions. Some of his characters are borrowed from these ancient tales, but others are wholly original creations. The reader follows the adventures of a young pig-keeper, Taran, who along with his friends—a princess, a harpist, and a wild twigcovered creature—attempt to rescue Hen Wen, the oracular pig of the wizard Dallben. On the mythic level the heroes encounter the dark lord of the underworld and meet the fairy folk who inhabit the hollow hills.