Book 10 for my 2026 goal of 36 books for the year! Catching up a bit now. As usual, my link to the book is through my bookshop.org affiliate account, which means I may earn a small commission if you buy from there.

Sometimes I don’t even remember when or why, exactly, I bought a book to read! After purchase, they get put on one of several “to read” piles throughout my house and I very often lose track of them for a while. While tidying up this weekend, however, I happened across What Stalks the Deep (2025), by T. Kingfisher, and it seemed like a perfect read for the weekend.

This is the third book in the Sworn Soldier series, after What Moves the Dead and What Feasts at Night, which I haven’t read. You might wonder why I started with the third book, and I wondered too when I came across my copy again, but then I read the book blurb and I understood: it’s about people venturing into a mine that may be haunted!

The novel follows the further adventures of Alex Easton, a nonbinary Sworn Soldier of the (fictional) country of Gallacia. In this book, at least, we are not given any real indication of Alex’s biological sex, and it is a nice aspect of the story that it doesn’t really matter! I imagine that Alex’s background is given more detail in the first two books, but here the novel just jumps right into the plot.

Alex has been summoned to America by their friend Dr. Denton to help with an urgent crisis. Denton’s cousin Oscar has gone missing while exploring the family-inherited Hollow Elk Mine, but only after sending three rather cryptic messages about his experiences. The first two messages hint at strange lights and strange sights in the deepest parts of the mine as well as some sort of creature stalking the tunnels. The third message is even more baffling: a short telegram telling Denton to disregard the previous two as mine gas-induced hallucinations!

Denton suspects that something unnatural has happened to Oscar, and calls on Alex for assistance. Denton and Alex has shared a previous preternatural experience (in What Moves the Dead), and so Denton believes that Alex is one of the only people who will be able to help without having to waste a lot of time convincing them that something is seriously wrong. (Alex’s military background is also a plus.) Along with their servants, Denton and Alex head to the mine, looking for Oscar in the mine and Oscar’s assistant in town. But Denton’s suspicions of an unnatural threat turn out to be true, and the group will find that there is more than toxic gas threatening them in the depths…

What Stalks the Deep is a delightfully fast-paced novel, clocking in at 170 pages, and was a nice change of pace from my previous read of Jeff VanderMeer’s Dead Astronauts. The tone of the book falls somewhere between horror and adventure and manages to keep the momentum going from the beginning to the end. I am happy to note, without giving any details, that the story went places that I definitely wasn’t expecting and kept me guessing to the very end. I managed to read the whole book in a single morning while having an iced tea at a local coffee shop!

I will likely look into more of Kingfisher’s books, and other volumes in the Sworn Soldier series — this was a fun and engaging read!