While continuing to express concerns with social equality and with ecology, this work introduces several new themes. As Alexander pointed out, in this second volume in the Prydain series "a darker thread runs through the high spirits." As a result the sense of danger is more immediate, the perception of evil more disturbing. One major theme is the heroism of self-sacrifice. In this novel the imminent danger to all humanity is the Black Cauldron, a vessel which permits the Dark Lord to bring his own dead soldiers back to life again to fight once more in their gruesome, unfeeling way. Two heroic young men, one a bard and the other a princely warrior, sacrifice themselves in the struggle against the powers of the cauldron.
Another new theme is that of corruption through contact with evil. Taran is no longer an innocent living a sheltered rural life but one who must deal with the pervasive presence of evil. He and his companions learn that self-sacrifice may be necessary to avoid the corrupting influence.
(The entire section is 172 words.)