The Black Cauldron (The Chronicles of Prydain) by Lloyd Alexander
This is the second book in the Prydain Chronicles. It is an excellent story just as the Book of Three and we again see Taran learning what it means to become a man. This book is still very appropriate for younger readers, but it also deals with some tougher issues like loss, betrayal and death.
Description:Even though Arawn Death-Lord's army of deathless warriors cannot be stopped by any known weapon, Taran and his companions are determined to capture the Death-Lord's means of creating more of these monsters. Taran will face the most difficult challenges and decisions of his life if he is to rid the world of the Black Cauldon.