Here is a list of The Chronicles of Prydain Books in Order.
The Book of Three (1964)
From the blurb:
Taran is desperate for adventure. Being a lowly Assistant Pig-Keeper just isn’t exciting. That is, until the magical pig, Hen Wen disappears and Taran embarks on a death-defying quest to save her from the evil Horned King.…
The Black Cauldron (1965)
From the blurb:
The peaceful land of Prydain is under threat. The evil Lord of Annuvin is using the dark magic of the Black Cauldron to create a terrifying army of deathless warriors. The Cauldron must be destroyed, and Taran joins Prince Gwydion and his faithful knights, Ellidyr and Adaon, in this perilous quest.…
The Castle of Llyr (1966)
From the blurb:
Master Dallben has decided it is time for Eilonwy, daughter of the House of Llyr, to learn to behave like a proper princess. He sends her away to the Isle of Mona but instead of training in the art of being a lady, Eilonwy falls into the hands of the evil enchantress, Achren, who wants to use Eilonwy’s magical powers for her own ends.…
Taran Wanderer (1967)
From the blurb:
Taran the Assistant Pig-Keeper has led heroic adventures and is a friend of princes, yet he is still troubled by his lowly status and determined to discover the secret of his true identity. He sets out to consult the powerful witches of Morva and the mysterious Mirror of Llunet.…
The High King (1968)
From the blurb:
In this thrilling climax of the classic fantasy The Chronicles of Prydain, Death Lord Arawn has stolen the black sword Dyrnwyn, the most powerful weapon in the kingdom. At the request of Prince Gwydion, Taran rallies friends both old and new to raise an army to march against Arawn’s terrible warriors.…