Owen is a highly anxious man living in a bland apartment in Pittsburgh. He lives with obsessive-compulsive disorder that manifests in severe, compulsive nail-biting. He harbors deep resentment toward his former friends, particularly Lore, whom he feels exploited their shared creative ideas for her own success. Despite his bitterness and tendency to self-isolate, he feels a lingering obligation to the childhood "Covenant" he shares with his estranged friend group.

Lore is a highly successful game developer based in Seattle who relies on microdosing mushrooms to maintain her creative edge. She presents a no-nonsense, highly capable exterior and functions exceptionally well in crisis situations. Beneath her confident facade, she struggles with feelings of isolation stemming from childhood neglect and relies heavily on the found family she built with her friends.

Nick is the unpredictable catalyst who reunites the estranged friend group by invoking their childhood "Covenant." He operates with a sense of urgent, aggressive momentum, often pushing his friends into uncomfortable situations without hesitation. As a teenager, he was fiercely protective of the group, but his adult self exhibits erratic behavior that immediately puts the others on edge.

Hamish is a former easygoing teenager who has grown into a tense, heavily muscled adult with a wife and three children. He survived a near-fatal drug overdose in college, an event that led him to adopt strict Christian values and a rigid workout regimen. Despite his outward stability, he suffers from immense internal guilt over his personal failings and his physical self-image.

Matty is the charismatic and ambitious fifth member of the childhood friend group whose disappearance twenty years ago fractured their bond. Unlike the others, he appeared to have a bright future and a relatively stable home life. His fateful decision to climb a mysterious staircase in the woods leaves his friends burdened with decades of trauma and unresolved questions.

Detective Doore is a local law enforcement officer tasked with investigating Matty Shiffman's vanishing. She is highly skeptical of the teenagers' identical stories and presses them for the truth, heavily suspecting that drug use or foul play is involved in the incident.

Marshie is a teenage girl encountered by the friends in a shifting room that reflects a 1990s bedroom. Covered in self-inflicted wounds, she is fixated on the boy who rejected her and serves as a terrifying, physical manifestation of adolescent pain and rejection.

Alfie Shawcatch is a World War II Army veteran who purchased a single-family home in a postwar development. Haunted by the horrors he witnessed during the war, he sought peace but instead allowed his despair to fester, resulting in a horrific act of domestic violence.

Bryan is a high school senior who routinely torments Hamish and the rest of the friend group. His relentless cruelty eventually prompts the friends to form their protective "Covenant" and retaliate against him.

Grady is a teenage boy who is the object of Marshie's affections. His dismissal of her feelings serves as the catalyst for her tragic end and her permanent, supernatural manifestation in the house.