The final Prydain book doesn’t feature Taran or his companions. Instead it’s a collection of six short stories about Prydain that flesh out some of the concepts and history of Lloyd Alexander’s world.
“The Foundling” expands on what the tree Witches told Taren about “Little Dallben.” With “The True Enchanter,” we get a vision of Eilonwy’s mother (I believe…perhaps an ancestor…I’ll admit that I get easily confused by lineages…don’t even get me started on Tolkein). The story I enjoyed the most was “The Sword,” which dives into some ancient Prydain history. The other stories are various myths and morality tales.
The book is quite short, and serves as a nice, if somewhat slight companion to the five books of Taran’s adventures.
I read the whole series in one volume, The Prydain Chronicles, which I believe I got from a book club many years ago. For Fantasy fans, I would definitely recommend give the series a read, especially if you’ve got youngsters to read it to.