What Stalks the Deep

• Author: T. Kingfisher
• Genre: Horror
• Publication Date: September 30, 2025
• Publisher: Macmillan Audio
• Series: Sworn Soldier #3

Thank you to NetGalley and Macmillan Audio for providing me with an ARC of this audiobook in exchange for an honest review.

The next installment in the New York Times bestselling Sworn Soldier series, featuring Alex Easton investigating the dark, mysterious depths of a coal mine in America.

Alex Easton does not want to visit America.

They particularly do not want to visit an abandoned coal mine in West Virginia with a reputation for being haunted.

But when their old friend Dr. Denton summons them to help find his lost cousin—who went missing in that very mine—well, sometimes a sworn soldier has to do what a sworn soldier has to do…

I’ve been eagerly devouring these novellas from the first book in the series, and now that it came to book three, I was beyond ready. Getting approved for the audiobook version was like the icing on the cake. Hopefully, this series keeps going for a while, because I really enjoy it. 

The audiobook is narrated by Avi Roque, who does a fantastic job. They voice Easton with exactly the right amount of snark and sass, and have come to symbolize the voice of Alex Easton to me. I loved how they made the story really come alive, just as they have for the previous two.

Kingfisher demonstrates her extreme versatility with genres, writing novels influenced by fairy tales, horror, folklore, and fantasy, yet making each story feel completely unique. This one veers a bit more sharply into horror than others I’ve read by her, but it was still engrossing and fascinating. There is a clear gothic vibe to the story, with the story taking place in an abandoned coal mine in West Virginia.

Easton isn’t thrilled about heading to America, and has zero desire to check out a haunted mine. But when their old friend Dr. James Denton asks for their help in finding a cousin who has disappeared in that mine, Easton can’t say no, and Easton and Angus find themselves traveling throughout America to reach this mine and dreading it the whole way, while still making funny and snarky commentary at every opportunity. But once they arrive and see how creepy it is, the tension increases noticeably. 

It is easy to see where at least some of the horror comes from. Heading down into a mine is enough to scare off plenty (yeah, me included), but if you’ve ever gone down into a cave system underground, you’ll recognize the sense of all those tons of rock above your head, almost pressing down. It also comes along with a feeling of claustrophobia, which is enough to be scary without a possible haunting. Obviously all that has nothing on the thing that is down in the mine, which makes it even easier for me to avoid ever stepping foot in a mine—this will live on in my head rent-free, just like the other monstrous imaginings of Kingfisher. 

Besides the fact that the story takes place in America, there are other things about this book that distinguish it from the earlier two in the series: the focus on a decaying mine, the unique nature of this monster as opposed to the more natural or folklore-based creature, and the way that Kingfisher juxtaposes the slow, creeping horror of the two earlier books with the claustrophobic darkness of a mine and an enemy they can’t even see. 

Overall, this was an outstanding read. I loved seeing how Easton copes with their past trauma with sarcasm and snark, although seeing Dr. Denton seems to bring some of that trauma to the forefront, since they met during the events of the first book. The supportive friendship that has developed between Easton and Angus, their gruff yet loyal assistant, is easy to see. I also really love the way that Dr. Denton has pretty much joined them as part of a found family. One of the strengths of this book is the normalization of nonbinary identities, at least within Gallacian society. Alex identifies as nonbinary, and when people learn about how widely accepted non-binary people are within Gallacia, they tend to be more accepting of it even in societies where it wasn’t normalized at that time, such as England and America. This is a fantastic exploration of different sub-genres of horror, along with how far we will go for our family. It is a close contender for my favorite of Kingfisher’s books, and it’s an easy recommendation to make.

Disclaimer: This post contains affiliate links, and I may earn a small commission at no cost to you if you purchase through my links.