1266. Eleanor of Castile, adored wife of the Crown Prince of England, is still only a princess when she is held hostage in the brutal Baron's Rebellion, and her baby daughter dies. Scarred by privation, a bitter Eleanor swears revenge on those who would harm her family - and vows never to let herself be vulnerable again.

As she rises to become Queen, Eleanor keeps Olwen - a trusted herbalist, who tried to save her daughter - by her side. But it is dangerous to be friendless in a royal household, and as the court sets out on crusade, Olwen and Eleanor discover that the true battle for Europe may not be a matter of swords and lances, but one fanned by whispers and spies . . .