The Forbidden Tower

This is the novel of four who defied the powers of the matrix guardians - fanatics who protected those powers so that the planet of the ruddy sun might never fall beneath the influence of materialistic Terrans.
The four who found themselves fused into a terrifying unity in that defiance were two men and two women.

The men were Damon Ridenow, a Comyn of the ruling caste, and Andrew Carr, the Earthman who had won for himself the right of clan-entry.