The Book of the Ancestor trilogy is a series of three fantasy novels by Mark Lawrence. It comprises Red Sister, Grey Sister, and Holy Sister. The three novels tell the story of Nona Grey, a peasant girl with mystical abilities. Red Sister was nominated for the 2018 David Gemmell Awards for Fantasy.

At the Convent of Sweet Mercy, young girls are raised to be killers. In some few children the old bloods show, gifting rare talents that can be honed to deadly or mystic effect. But even the mistresses of sword and shadow don't truly understand what they have purchased when Nona Grey is brought to their halls. A bloodstained child of nine falsely accused of murder, guilty of worse, Nona is stolen from the shadow of the noose. It takes ten years to educate a Red Sister in the ways of blade and fist, but under Abbess Glass's care there is much more to learn than the arts of death. Among her class Nona finds a new family—and new enemies. Despite the security and isolation of the convent, Nona's secret and violent past finds her out, drawing with it the tangled politics of a crumbling empire. Her arrival sparks old feuds to life, igniting vicious struggles within the church and even drawing the eye of the emperor himself. Beneath a dying sun, Nona Grey must master her inner demons, then loose them on those who stand in her way.

In Mystic Class Nona Grey begins to learn the secrets of the universe. But so often even the deepest truths just make our choices harder. Before she leaves the Convent of Sweet Mercy Nona must choose her path and take the red of a Martial Sister, the grey of a Sister of Discretion, the blue of a Mystic Sister or the simple black of a Bride of the Ancestor and a life of prayer and service. All that stands between her and these choices are the pride of a thwarted assassin, the ambition of a would-be empress wielding the Inquisition like a blade, and the vengeance of the empire’s richest lord. As the world narrows around her, and her enemies attack her through the system she has sworn to, Nona must find her own path despite the competing pull of friendship, revenge, ambition, and loyalty.

The ice is advancing, the Corridor narrowing, and the empire is under siege from the Scithrowl in the east and the Durns in the west. Everywhere, the emperor's armies are in retreat. Nona faces the final challenges that must be overcome if she is to become a full sister in the order of her choice. But it seems unlikely that Nona and her friends will have time to earn a nun's habit before war is on their doorstep. Even a warrior like Nona cannot hope to turn the tide of war. The shiphearts offer strength that she might use to protect those she loves, but it's a power that corrupts. A final battle is coming in which she will be torn between friends, unable to save them all. A battle in which her own demons will try to unmake her. A battle in which hearts will be broken, lovers lost, thrones burned.