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.Holy sister completes the Book of the Ancestor trilogy that began with Red sister and Grey sister. A ground-breaking series, it has established Mark Lawrence as one of the most exciting new voices in modern speculative fiction.