In 1135, during the civil conflict between the usurper, King Stephen and "Empress" Matilda (the daughter of Henry I), two cousins, Raymond and William (unavoidably, one of the many "Williams" in the story), are born and raised at Carew, in south-west Wales. Their growth through infancy to maturity becomes an important part of the theme of "They Served the Devil's Brood." It is a critical time in England and Wales, as the barons are torn between loyalty to either faction, as well as having to deal with an increase in Welsh opposition to their presence. Calls are also being made for their knights and vassals to join the Crusade against the "infidels", who have taken control of the Holy Land. Henry Plantagenet, the son of Matilda, enters the fray as a youth, but has to be content to wait till Stephen, bereft of a viable heir, agrees to name Henry as his successor. The Welsh Church is also facing increased demands from the centralised hierarchy of Rome. As Henry II takes over the reins of government, his influence on all involvedbecomes apparent. He is kept busy - and with him all his servants - travelling his domains in France and England. An exiled minor Irish king appeals to Henry to help him recover his rightful place and territory. He is given permission to gather such help as he can from the Norman-Welsh barons. Richard de Clare ("Strongbow") - rather "down-on-his-luck" at the time - responds. It takes some time, but with Raymond's help, plus that of Raymond's relations, the FitzGeralds, they invade the south-east corner of Ireland. Raymond proves to be a capable warrior and brilliant commander, but has to struggle with his own troubles, as he seeks the hand of the higher-born sister of Richard, Basilia de Clare.