Bela is an observant eight-year-old girl spending her summer break at home. She is highly attuned to the emotional atmosphere in her house and deeply desires her parents to remain happy together. Because she lacks close companions her own age, she initially views the supernatural entity in her bedroom as a friend and keeps its presence a secret.

Russ, whom Bela calls Daddo, is a relentlessly optimistic father who works from his home office. He prefers to keep the peace and acts more like a friend to Bela than a strict parent. He intentionally ignores the growing distance between himself and his wife, favoring a cheerful facade even when problems arise.

Ursula works outside the home and feels suffocated by the demands of motherhood and domestic life. She often returns home late, using alcohol to manage her frustrations. Her unhappiness creates a tense atmosphere in the home that Bela easily detects, despite Ursula's attempts to hide it.

Ruth is Ursula's mother, a petite but formidable woman who lives in a small, cozy home. Unlike her daughter and son-in-law, she refuses to pretend everything is fine when trouble arises. She prioritizes truthfulness and immediately takes charge when she realizes Bela is in danger.

Other Mommy is a mysterious, monstrous entity that resides in Bela's closet. She mimics domestic behaviors to present herself as a friend to the lonely eight-year-old. She is relentless in her single goal: convincing Bela to grant her permission to enter the little girl's heart.

Lois is a local woman with red hair and large glasses who claims to possess a sensitivity to the supernatural. She runs a weekly Friday group dedicated to discussing paranormal phenomena. Despite the skepticism of others, she genuinely wants to assist Bela with the disturbances in the house.

Deb is a young girl from Bela's neighborhood and her only real peer. She plays imaginary games involving swords and monsters but becomes quickly overwhelmed when Bela introduces real fears into their conversation.

Carly is Deb's mother and a local neighborhood parent. She provides a listening ear for Ursula during a difficult emotional moment at the playground.

Kelvin is a local teenager hired to supervise Bela during social gatherings. He is friendly, dances with Bela, and acts as an older, reliable companion to her while the adults socialize downstairs.

Dr. Smith is Bela's pediatrician. He asks gentle, thorough questions about Bela's accident, inadvertently making Ursula defensive about her attentiveness as a parent.

Dan is a neighbor of Russ and Ursula who has a new baby. He tries to be polite when his neighbors experience an emergency but ultimately prioritizes the safety and quiet of his own home.

Amanda is Dan's wife and a cautious neighbor. She becomes highly unsettled when Ursula and Russ bring their domestic terror into her living room in the middle of the night.

Marsha is a friend of Bela's parents who becomes hysterical at a gathering. She is the first adult to witness the physical presence of the entity lurking in the house, causing a major disruption.

Frank is a man with a private, hidden connection to Ursula. His sudden and tragic situation severely escalates the danger surrounding Bela's family.

Evelyn is an older woman whose children have moved out, leaving her with a large, empty house. She offers hospitality to her old friend's family without knowing the true, terrifying reason for their sudden visit.

Brian is a tall, abrasive paranormal investigator hired by Russ. He is entirely self-motivated, seeking only to confirm the existence of the supernatural for his own satisfaction rather than actually helping the family.

Kyle is a member of Lois's Friday group dedicated to the supernatural. He is hesitant about interacting with an unknown entity but relays a frightening message to Bela during a séance.

Milky is Grandma Ruth's small, affectionate dog. The pet provides a momentary source of normal, innocent comfort for Bela during her family's frantic escape.

Pester is the family cat. Bela uses Pester's behavior as a frame of reference to understand the escalating, animalistic demands of the entity in her closet.