The scarlet seed - Edith Pargeter

In the castle of Parfois, glaring down over the debated lands of the Welsh border, young Harry Talvace is held prisoner by his father's sometime patron and later destroyer, Ralph Isambard. Captive and captor, bound together by implacable hatred and reluctant affection, seem doomed to stalemate.

Then the threat of civil war in England lays Isambard open to his enemies, and Harry abruptly reaches self-knowledge and maturity. The story reaches a strange and violent climax as the principal characters are drawn together in the final siege of Parfois under the towering shadow of the first Harry's master-work, the great church he gave his life to finish..