Prince of darkness - Sharon Kay Penman

DECEMBER, AD 1193. England lies uneasy, a land without a king. Richard the Lionheart languishes in an Austrian dungeon and his brother John hungers for the crown. In the Lionheart's stead, Eleanor of Aquitaine rules. She is determined to prevent the outbreak of civil war, but the land is riven by treachery and there are few men she can trust.

Justin de Quincy is one of the few. Sharp-witted, bastard-born, he is the Queen's most trusted agent, a foil to John's machinations. But now John himself has asked for de Quincy's aid. A powerful conspiracy threatens the course of history and de Quincy will have to prove his mettle - or find an early grave - as he searches for its dark heart.