In this third installment of the Sworn Soldier series, nonbinary retired soldier Alex Easton reluctantly travels from Europe to the United States with their companion, Angus, to help out their old friend, Dr. Denton, who is experiencing a problem with potential supernatural implications in West Virginia.

Before I dive into the story --- and there is so much to savor here --- I must make note of something that T. Kingfisher includes at the top of her Acknowledgements. She indicates that her favorite H.P. Lovecraft story is AT THE MOUNTAINS OF MADNESS and that some of the elements and beings I will describe from WHAT STALKS THE DEEP were her attempt to make a shoggoth from spare parts lying around the Earth. This may not make sense to those uninitiated to the great Lovecraft. But if you know, you know!

"WHAT STALKS THE DEEP moves so deftly between horror, thriller and dark fantasy that it is impossible to categorize it. The ideas and imagery are just brilliant."

Alex arrives in America fresh after the war with Spain with which she was involved. Their ship steams into Boston where they meet up with Denton before proceeding to West Virginia, where the true reason for their visit becomes apparent. Denton takes them to the allegedly haunted coal mine where his cousin, Oscar, recently disappeared under mysterious circumstances. He introduces them to his colleague, John Ingold, a Frenchman who may be of assistance as they enter the mine. Hollow Elk Mine has had a long tradition that includes much talk about supernatural presences deep within its bowels.

As the group proceeds into the mine, they find themselves in an area that appears to be covered in small mirrors, later to be identified as some sort of crystals that no one has ever seen before. It reminds Alex of the crawling malignancy they experienced within the Usher house in the opening installment of the series. Rumors abound among the locals about a powerful bear that may be responsible for several deaths in the area. Could this bear have gotten into the mine and confronted Oscar?

They come across a note that seems to scare anyone who reads it into leaving or face great danger. Upon discovering a badly mutilated corpse, they wonder if a bear or some other animal may have been responsible. When they enter into the purported area of mirrors, they find a level of rare crystallization that Ingold compares to a creature like the cuttlefish --- with the walls changing and undulating with sound, color and shape all around them. 

The story takes a huge shift in tone when the group comes across what they believe to be the missing man. He claims not to be able to speak due to an injury and writes out his words on a board. He is also wearing a big pair of goggles that cover his eyes. This being is not Oscar but something akin to the creatures they find deep in the mine that may have been able to imitate his form --- with the exception of eyes completely without any pigment. It seems friendly and wants to be called Fragment. They all learn much from each other, and a major decision needs to be made about how to handle their relationship going forward. Even more precarious is how to describe this discovery with the rest of the world. 

WHAT STALKS THE DEEP moves so deftly between horror, thriller and dark fantasy that it is impossible to categorize it. The ideas and imagery are just brilliant. They truly set T. Kingfisher apart from other authors in these genres, thus making her work enjoyable to a wide swath of readers. I hope we see more of Alex Easton and company in the future.