This Holy Sister review contains spoilers for the previous Book of the Ancestor books, but only minor spoilers for the third book in the trilogy.

First off, if you haven’t read Red Sister or Grey Sister (the first two books in the Book of the Ancestor trilogy), you need to drop everything and read them now. This is my favorite series to come from this author so far. To put that in context, I have already read and loved Mark Lawrence‘s previous two series: The Broken Empire and The Red Queen’s War.

Here’s what you may have missed: Nona was an orphan taken in by the Sweet Mercy convent as a child. The novices at the convent are trained in four different classes and eventually choose one direction to pursue, whether it’s the magical otherworldly ways of the Mystic Sister, the traditional religious study aim of the Holy Sister, the combat training of the Red Sister, or the assassination stealth training of the Grey.

Nona is proficient in three areas, a rare “triple blood” that almost marked her as the Chosen One in early storylines. In a rare (and refreshing) twist on the Chosen One trope, she turned out not to be the Chosen One, and the whole prophecy was faked to begin with.

read more: Red Queen by Mark Lawrence Review

The Book of the Ancestor series take place on a world called Abeth, which was settled by four races of people untold centuries ago, and now is falling victim to an encroaching ice age. The remaining civilization lies in The Corridor, a strip of land about fifty miles across around the center of the planet. As the ice walls of the North and South close in, the different nations on the world get more desperate for land and resources, leading to the war that comes to its peak in this final book.

In Holy Sister, Lawrence continues tradition of flashing forward and backward to bring the story full circle, though not to the exhaustion of the reader. It’s well implemented and a clever way to reveal details about what happened between the climactic ending of Grey Sister and the beginning of this story — but only when necessary. Details and revelations are held back from us for maximum effect later when Nona clues others in to the elaborate plans of Abbess Glass.

Lawrence’s world building gives rich detail of previous civilizations, but only peeling back the layers when necessary. There’s still an air of mystery about Abeth’s beginnings and what happened to the Missing, but enough clues to make your own connections.

read more: Grey Sister by Mark Lawrence Review

The machinations applied by Abbess Glass that shape future events are reminiscent of Dumbledore’s long game in the Harry Potter series. That and the fact that part of the story takes place in a school that explores some magical properties is about the end of the similarity. The Book of the Ancestor series is in its own class entirely, as fresh as it is fun to read, with deepening mysteries and incredible wisdom.

In the flashbacks, we see Nona and Zole’s trek out on the ice, pursued by an army. They come upon a darkness in the ice, filled with devils and dark chasms that can swallow a person whole and lead to their remains never being discovered. The description of the ice caves and the hidden passages below the Rock of Faith make for an impressively claustrophobic reading experience; it’s a horror different from an enemy swinging a sword — though there are plenty of those as well.

Another strength of this series are the friendships. Amidst all the pressures these girls face — from the approaching enemy, the trials they go through during their education, and the literal end of the world coming in the form of ice walls — these girls form deep, emotional bonds with each other, and develop a loyalty not just to their religion but to the betterment of each other. It’s really sweet. Especially since the other times they’re learning how to eviscerate the enemy or not explode when walking the mystical Path.

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Holy Sister‘s most fascinating and perhaps integral theme is the exploration of power and its ability to corrupt. You see it in the political side of things, you see it in the danger of losing control of one’s powers and dying as a result (something that can happen if you misstep on the Path). You also see this in connection with the shiphearts or Old Stones, devices that amplify powers and may have once powered the ships that brought the people to Abeth.

Being in the presence of a shipheart makes a person stronger in their gifts — at the cost of harming their sanity and splitting their personality into devils. It’s quite a price to pay, but Nona and her friends end up in the presence of more than a couple shiphearts in their ultimate journey of this book. At some point, you see our main characters gain access to something of immense power, and the temptation to use, misuse, or not use it at all, is a major turning point.

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A lot of moral ambiguity takes place in order for our characters to survive. Whether they can do that and keep their souls intact — well it’s time for you, dear reader, to discover that on your own. The ending — I dare not give you anything crucial away — left feelings of sorrow yet completion. So much takes place in the last hundred pages or so, leaving the reader no choice but to keep turning pages until the conclusion.

Holy Sister is a worthy end to a great series, bringing Nona’s tale full circle. I’m sad its over, but following this story’s path was a mystery worth exploring.

Bridget LaMonica is a contributor at Den of Geek. Read more of her work here or follow her on Twitter @BridgetLaMonica.