The Book of Three is the Newbery Award-winning first title in Lloyd Alexander’s classic and excellent children’s series, The Chronicles of Prydain. (Really this is just a classic series, for both adults and children, IMO…)
Book has dropped to £0.99 at Kindle UK. Note that all five titles in this series were on sale at Kindle UK about a year ago, so check carefully before you buy.
Buy at Kindle UK