What Stalks the Deep (2025) is the third novella in the Sworn Soldier series by T. Kingfisher, otherwise known as American author and artist Ursula Vernon. Kingfisher is known for her Gothic retellings, dark humor, and character-driven storytelling. A work of speculative fiction, What Stalks the Deep follows retired Gallacian soldier Alex Easton as they investigate a supernatural disturbance in an abandoned coal mine in West Virginia. Set against a backdrop of extractive mining practices, the novella examines how trauma shapes perception while exploring the concepts of social conformity and the consequences of isolation.

This guide uses the e-book version of What Stalks the Deep written by T. Kingfisher and published by Tor Publishing Group in 2025.

Content Warning: The source material and guide feature depictions of gender and transgender discrimination, antigay bias, mental illness, animal death, substance use, graphic violence, and death.

Plot Summary

Easton, born female, is a Sworn Soldier from the fictional European country of Gallacia. At the request of friend and fellow veteran James Denton, Easton and their batman, Angus, a soldier assigned to assist a commissioned officer, are traveling to Boston. Having faced a destructive sentient fungus with Denton in Ruravia, Easton fears a similarly dangerous supernatural encounter awaits them.

Arriving in Boston, Easton and Angus meet Denton’s assistant, Kent, who takes them to see Denton and his friend John Ingold. Denton explains that his cousin, Oscar, has disappeared after exploring the abandoned Hollow Elk Mine in West Virginia, which Denton inherited. He shares letters from Oscar, who had been staying at the mine with his assistant, Roger, and Roger’s large watchdog, Thunder. Oscar’s letters describe strange sounds, red glowing lights, and an unusual chamber within the mine.

After receiving the latest letter, Denton had traveled to the mine, finding it deserted. Upon returning home, Denton received a long telegram explaining Oscar had been poisoned by gases in the mine and had hallucinated the strange events. Although the others suggest Oscar has likely been murdered, Denton insists that he sensed something strange about the mine that reminds him of the supernatural events in Ruravia.

Easton agrees to travel to the mine. The trip takes longer than Easton expects, and they note signs of industrial exploitation along the journey. As they arrive at the mine, Easton is struck by the large number of dilapidated buildings. They find Oscar’s camp and briefly enter the mine. Ingold, a chemist, warns them of potential deadly gases, including firedamp, demonstrating by lighting the mine wall on fire. Without headlamps, they decide to return to the surface and agree that no one is to enter the mine alone.

The group travels to the nearby town of Flatwood. Easton and Ingold go to the telegram office, where the clerk describes her encounter with the strange, silent man who had sent the telegram the month before. After rejoining Denton and Angus, who have located Roger, they are questioned by Roger’s protective neighbor, Elijah, and directed to his house. Roger is asleep when they arrive, having been drinking excessively. He’s unable to tell them what happened to Oscar, but insists it has something to do with a red light in the mine. While they are speaking, Easton tries to greet Thunder and is disturbed by Thunder’s unnatural response.

The next time the group enters the mine, they reach an area with suffocating blackdamp gases, and Ingold starts to map the mine. Easton hears a strange “squelching” noise and warns Ingold, urging him to turn away from the sound. However, they move to an area with blackdamp and when Easton begins to hallucinate, Ingold forcibly drags them to safety.

Later, they return to the mine searching for the source of the noise but find a red light and a pile of debris blocking a mineshaft instead. Clearing the pile enough to see over the top, they find a second mound of rocks and an empty mining outfit laid out face down on the ground. While examining the suit, Easton finds a receipt for the telegram.

The next day, someone leaves the group a note warning them of danger in the mine. However, they continue to clear debris. In the night, Easton wakes to use the bathroom. When he sees the red light, he impulsively chases it until he discovers a flat, human-like creature. They return to the surface, where they tell the others about the strange sight. Elijah arrives seeking Denton’s help because a woman named Louisa, has been attacked and badly injured, and another man, Lee Mason, has been killed.

Easton goes to Flatwood with Denton and Ingold. While Denton is helping Louisa, Easton pets a brown hound, noting how different this dog is from Thunder. When Denton finishes his work, Easton walks over and knocks on Roger’s door, but no one answers and Thunder does not bark.

The next day, Denton returns to the mine early to clear debris, and Kent tells Easton he is concerned about his employer’s behavior. Easton enters the mine to find Denton has cleared the rock and found a narrow tunnel. When Denton tries to enter the tunnel, Ingold stops him, but Denton insists he must search for Oscar despite the risk. He descends for a time then returns and tells the others to join him.

As Easton descends the undulating and spiraling tunnel, their fear intensifies. At the bottom of the tunnel, they find a large cave with a strange pearl-like floor. While looking at their likeness in the floor, Easton realizes the floor is mimicking them rather than reflecting their appearance. Disturbed, Easton insists on returning to camp, but when they get to the top of the tunnel, they see the red light.

Denton chases after the light, and when Easton catches up they see Denton with someone who looks like Oscar. Angus joins, pointing a gun at the person and forcing them to remove their goggles. The entity—which later names itself Fragment—explains that he means no harm and has written them a letter.

They return to camp, where Fragment continues to explain that he is part of a Wholeness that lives underneath the protective floor of the cave. Fragment is a filter feeder who had been separated in a mining explosion and has been living in the mine ever since, learning from the humans he observes. He tells them a Sentry had been sent out long ago but had never returned.

Denton asks for a private word with the others to discuss Fragment. Ingold explains that Fragment is likely not dangerous; however, Denton is skeptical, questioning how to kill the entity. Ingold unwillingly admits that fire would likely kill Fragment, but he insists Fragment needs their help reuniting with the Wholeness. That evening while Easton is speaking to Denton, an unidentified creature attacks the horses. Although Angus shoots the creature, they are unable to find a blood trail in the morning.

Denton’s distrust of Fragment continues, worsened by Ingold’s fascination with Fragment. Easton goes into the mine with Fragment as Fragment visits the Wholeness. As they exit, they see Roger and Thunder, and Thunder charges, pushing Easton and Fragment back into the mine. There, Thunder morphs, revealing itself to be the Sentry sent out long ago. Angus and Ingold rush to help, covering the Sentry with oil and burning it. Part of the Sentry escapes the flames only to be surrounded by Fragment. Fragment eventually separates and tells Easton and the others that the Sentry had refused to unite with him. They hypothesize that the Sentry has been corrupted by prolonged isolation.

Easton, Denton, Ingold, and Angus help Fragment, obtaining a diamond bit so they can drill through the floor of the cave. While working in the mine, Easton offers to fetch water when they run low. As they walk through the mine, they find a remnant of the Sentry, which pursues them. Easton runs to an area with firedamp, where the Sentry begins attacking them, stabbing into their legs with broken bits of bone. Easton flicks their lighter, igniting the firedamp.

Injured, Easton fades in and out of consciousness while their friends are rescuing them. Later, they learn that Fragment had funneled fresh air to them and had lined the inside of their leg wounds to prevent Easton from bleeding out before they could be brought to the surface. During the event, Denton had worked closely with Fragment, and while he is still skeptical of the Wholeness, he now trusts Fragment.

The rest of the Sentry is found and destroyed, and they successfully open a hole in the cave floor so Fragment may rejoin the Wholeness. Roger will stay to guard the mine with Elijah’s support, while Easton agrees to extend their visit to America as long as it does not involve any moreanymore mine exploration.