The final volume in The Chronicles of Prydain circles around the final battle between all good and evil forces in Prydain. The High King begins with Taran’s homecoming to Caer Dallben, where Princess Eilonwy and his other companions await him.
However, he is shocked to behold Prince Gwydion near death after an encounter with Arawn, the Lord of Annuvin. Moreover, Gwydion’s enchanted sword, Dyrnwyn, has been stolen from him by Arawn’s minions. Even though all swear that Dyrnwyn must be immediately recovered, treachery in Cantrev Cadiffor persuades Gwydion to abandon that quest and instead begin preparations for battle against Arawn. Taran finally takes his stand among men as a leader and a warrior. Summoned by the High King Math himself, Taran is ordered to rally the Free Commots to meet at Caer Dathyl for that final battle. All the companions are together again, but death and sacrifice will separate them forever unless Arawn is decisively defeated.
The High King is considerably the most complex novel in the series due to the involvement within the plot of all characters introduced throughout the previous four volumes. Platonism is an evident part of the storyline as Taran rises to become the anticipated philosopher-king of all Prydain, the High King; he is a man who does not want to be a king, and therefore must be the king. Taran’s difficult journey from adolescence to manhood has educated him; his adventures and his friendships have taught him wisdom and justice that make him worthy to ultimately draw Dyrnwyn and defeat Arawn’s deathless Cauldron-Born. His destiny is deeply intertwined with Prydain’s, and the final choice he makes between eternal life and mortality proves this. The Chronicles of Prydain is an epic series in its own right, comparable to The Chronicles of Narnia in the extent of its allegorical and philosophical content. The High King itself is a stirring conclusion to the land of Prydain and its inhabitants, with morality and virtue overcoming all enchantment.
Part 5: Lloyd Alexander’s ‘The Chronicles of Prydain’, Examiner.com