The Chronicles of Prydain #1 The Book of Three by Lloyd Alexander*

Taran lives a simple life in Caer Dallben as an Assistant Pig Keeper (an oracle pig named Hen Wen!) with Dallben (the master) and Coll.  Periodically Dallben reads from The Book of Three where Taran hears about the history and heroes of Prydain.
Now it seems like the Horned King who serves the evil King Arwan is on the move.  Hen Wen senses the evil and escapes from her pen.  Taran pursues but soon finds himself on an unexpected adventure where he meets a variety of interesting characters.
Readers who love The Lord of the Rings will enjoy this journey/quest adventure story.
A phrase I want to remember from the book is "there are times when the seeking counts more than the finding." (pg. 185)
My fourth grader is currently reading the series and is on book #4.
*Highly recommend.
-I own the series (#1-5).
Guided Reading Level: U (5th grade)