The Chronicles of Prydain 01: The Book of Three

Taran dreams of fighting heroic battles instead of being an Assistant Pig-Keeper until Hen Wen, the magical pig, disappears.
With the land of Prydain under threat from the Horned King, and Taran searching for Hen Wen, he is drawn into a deadly quest. Coming face-to-face with warriors and witches Taran is about to learn what it takes to be a hero.