Denton is a retired Army surgeon and Easton’s close American friend, bound to Easton through war and their past adventures in Ruravia. He summons Easton to America because he believes the disturbance at Hollow Elk Mine may be supernatural, specifically seeking someone who will not dismiss the possibility of “terrible things in the earth” (7). Like Easton’s, Denton’s perspective is shaped by prior traumas. His experience with the fungus predisposes him to interpret inhuman sentience as a threat. His guardedness extends beyond the supernatural, as he attempts to disguise his romantic relationship with Ingold as friendship.

Denton’s character arc centers on fear and its impact on moral judgment. Having witnessed both war and the devastation in Ruravia, Denton struggles to believe in the possibility of benign inhuman life. His fear culminates when he urges the others to destroy Fragment: “‘We could end all this now […] We could stop it and just go home’” (149). The repetition of “we” and the concept of “home” frame his impulse as an exhausted cry for relief. Crucially, his companions intervene when his fear overwhelms him, preventing an irreversible decision and highlighting the importance of human connection and community.

Denton’s final transformation arises in a moment of shared crisis with Fragment. When Easton is injured, Denton works alongside Fragment to save them—"it stopped mattering that he was basically just a tube and a pair of hands” (167). This cooperation reshapes Denton’s perception, allowing him to recognize Fragment’s personhood. Through Denton, the narrative demonstrates how trauma can constrict ethical judgment, but also how connection and shared survival can restore it.

John Ingold is an American chemist and Denton’s romantic partner. Easton first describes him as having “the tan skin and straight black hair that I associate with the native people of the continent,” noting that “when he opened his mouth, his Boston accent was so thick that you could stand a spoon up in it” (6). The description situates Ingold within the social world of the American setting, while subtly emphasizing his layered identity. His relationship with Denton began when he warned Denton to ventilate his apartment after a chemical mishap. Like Denton, he aims to preserve the secret of their romance, positioning him within a socially constricting environment, underscoring the theme of American Conformity Versus Otherness.

Ingold functions as the novella’s voice of reason. While Denton interprets events through the lens of trauma, Ingold approaches the unknown through analysis and observation. Easton notes, “He was, above all, interested in things. He wanted to know why things worked […] The world was an endless source of fascination and wonder” (55). While Denton distrusts Fragment, and Easton is repulsed by him, Ingold is genuinely curious, asking questions and offering scientifically-informed hypotheses rather than jumping to conclusions about Fragment’s potential danger.

Ingold, though a major character in the novella, remains relatively static. From the beginning, he is inquisitive and open-minded, encouraging his peers to follow suit. Through Ingold, Kingfisher positions rational inquiry as capable of interrupting fear and premature judgment.

The Wholeness is a long-lived sentient life form. Fragment explains that the Wholeness once lived on the surface of the ocean before seeking refuge underground during an ice age. The pearlescent floor of the cavern functions as a defensive shell, capable of imitating its surroundings through chromatophore-like cells as a line of self-defense. The Wholeness can divide, reintegrate portions of itself, and exchange memory with other Wholenesses.

Thunder, who is eventually revealed to be the Sentry, demonstrates the consequences of separation from that collective identity. Sent out decades earlier, the Sentry never returned to the Wholeness and instead lived in isolation. Unlike Fragment, who seeks reunion, Thunder resists reintegration and declares that he does not wish to be whole. His violence reflects adaptation through domination, as he gathers bones to reinforce his body and kills beyond necessity. Ingold suggests that extended loneliness may have impacted the Sentry’s sense of self. Thunder’s antagonism, therefore, is complicated by trauma. Through Thunder, the novella explores how trauma and isolation, when adopted into identity, can result in monstrousness, highlighting The Boundary Between Monstrosity and Personhood.

Fragment, by contrast, represents an alternate response to separation. Unintentionally cut off from the Wholeness during a mining explosion, he survives by observing and avoiding contact with humans. Rather than fortifying himself through violence, as Thunder does by killing excessively, Fragment learns language and studies behavior to communicate. Even when confronted by Denton’s overt hostility, Fragment remains neutral, submitting to questioning and requesting help.

Through the contrast between Thunder and Fragment, Kingfisher complicates the concept of monstrosity. Both originate from the same inhuman life form, but one is shaped by isolation and violence while the other seeks connection and reintegration. Together, the Wholeness, Thunder, and Fragment challenge fixed definitions of identity, presenting personhood as arising from connection rather than biological form.