AD 664: Sister Fidelma finds herself in the seaport of Genua, en route from Rome back to her native Cashel. Her old teacher, Brother Ruadan, lies dying in the abbey of Bobium - an isolated abbey in a disturbed country where even the Christians are in bloody conflict with one another and the worship of the pagan gods often prevails. Fidelma is determined to see Brother Ruadan before he dies. But from the moment she enters the beautiful valley of the Trebbia, there is danger on every side.

Her dying teacher's last words send her off on her most dangerous adventure where murder follows murder and a vicious civil war threatens before an extraordinary conspiracy is revealed. And from the start, Fidelma is on her own...