Holy Sister

Holy Sister is a fantasy novel by the American-British writer Mark Lawrence, published in 2019. It is the third and final book of the Book of the Ancestor trilogy and concludes the story of Nona Grey.

The book opens with the empire in retreat. The ice is advancing, the Corridor is narrowing, and the empire is being attacked by the Scithrowl in the east and the Durns in the west, while its armies fall back everywhere. Nona Grey is still a novice when the war reaches her order, and the final challenges that stand between her and the rank of full sister have to be faced while everything around her is coming apart. The shiphearts offer a source of strength that she could use to protect the people she loves, but it is a power that corrupts whoever takes it up. A final battle is coming in which she will be torn between her friends, unable to save all of them, and in which her own inner damage will try to unmake her. The trilogy began with her arrival at the convent as a child, and this volume brings that story to its close.

Lawrence writes fantasy that mixes the training of a religious order with the politics and warfare of an empire, and the series is set in a world being slowly overtaken by ice.