Henry VI, son of the all-conquering Henry V, was one of the least able and least successful of English kings. His long reign, which started when he was only nine months old, ended in catastrophe, with the loss of England's territories in France and a bankrupt England's long decline into civil war: the wars of the Roses. Yet, failure though Henry undoubtedly was, he remains an enigma. Was he always, as he became in the last disastrous years of his...