Born of an incestuous relationship between King Arthur and his half sister, the evil sorceress Morgause, the bastard Mordred is reared in secrecy. Called to Camelot by events he cannot deny, Mordred becomes Arthur’s most trusted counselor -- a fateful act that leads to the "wicked day of destiny" when father and son must face each other in battle.
The dark forces that were repulsed in "Out of the Silent Planet" and "Perelandra" are massed for an assault on the planet Earth itself. Word is on the wind that the mighty wizard Merlin has come back to the land of the living after many centuries, holding the key to ultimate power for that force which can find him and bend him to its will. A sinister technocratic organization is gaining power throughout Europe with a plan to "recondition" society, and it is up to Ransom and his friends to squelch this threat by applying age-old wisdom to a new universe dominated by science.