Kara is a 34-year-old freelance graphic designer who relocates to Hog Chapel, North Carolina, after her marriage quietly ends. Seeking a temporary haven from her displaced life, she takes over the daily operations of her uncle's idiosyncratic museum. She approaches unusual situations with heavy skepticism and attempts to impose order on her strange surroundings by creating spreadsheet-based inventories and focusing on mundane tasks.

Simon is an eccentric barista in Hog Chapel who quickly becomes Kara's closest confidant. He identifies as a genetic chimera, possessing his fraternal twin's left eye, which gives him a unique form of color blindness and an unusual visual perception of the world. He embraces bizarre concepts readily and provides steadfast loyalty to Kara when they uncover the impossible concrete corridor.

Uncle Earl owns and operates the Glory to God Museum of Natural Wonders, Curiosities, and Taxidermy. He is a deeply kind man whose eclectic worldview comfortably accommodates Christianity alongside cryptozoology and conspiracy theories. Suffering from severe knee and back pain, he leaves the museum in Kara's care while seeking double knee surgery in Charlotte.

This collective, non-humanoid entity inhabits and controls the mysterious environment accessed through the museum wall. They hunt by sensing human thoughts and display an inscrutable, predatory curiosity toward intruders. The entities operate entirely outside human morality or logical comprehension, leaving distinct cone-shaped depressions in the ground where they strike.

Mark is Kara's ex-husband, representing the conventional, mundane life she leaves behind. He maintains a shallow social media presence focused on platitudes about moving bravely into the unknown. This contrasts directly with the tangible and terrifying unknowns Kara actually faces.

Martin is a former park ranger who inadvertently entered the willow world through a portal he describes as a kudzu cathedral. He serves as a crucial source of exposition, warning Kara and Simon about the predatory nature of the entities that govern the dimension and explaining how they track their prey through thought.

Beau is the resident cat at Uncle Earl's museum. He acts as a grounding element of normalcy within the eclectic setting, relying on his animal instincts to patrol the building and react to unusual disturbances or sounds.

Woody is an unseen associate of Uncle Earl who regularly supplies the museum with unusual artifacts. He is responsible for shipping the strange corpse-otter carving to Hog Chapel, which sets the central events of the story into motion.

Prince is a taxidermied Roosevelt elk head that holds nostalgic value for Kara from her childhood visits. He represents the benevolent eccentricity of the museum's collection and the lingering presence of Uncle Earl's affection.

Kara's mother maintains a somewhat strained and anxious relationship with her daughter. She assists the family by driving Uncle Earl to Charlotte for his double knee surgery, thereby leaving Kara to manage the museum entirely alone.

Mr. Bryce is a neighbor and friend of Uncle Earl in Hog Chapel. He keeps a watchful eye on the local businesses and alerts Kara's family when the museum uncharacteristically fails to open during regular hours.

Singer is a woman from another dimension whose experiences are recorded by an unnamed soldier. Her documented survival strategies provide critical insights into evading the thought-sensitive entities that populate the alternate world.