A young marchioness is murdered during a royal gathering and discovered in the arms of the Prince Regent. The necklace around her throat once belonged to Sebastian's mother, who was believed to have died at sea, giving him a personal reason to investigate the victim's movements and the people closest to the court.
As more deaths follow, Sebastian uncovers links between Welsh nationalism, disputed royal legitimacy and his mother's disappearance. The inquiry draws him into a conspiracy whose architects are willing to kill again to destabilise the succession and bring down the monarchy.