Oliver Thredson is a psychiatrist. At first, he appears to be one of the few genuinely rational and compassionate people at Briarcliff Manor. He is intelligent, calm, professional, and seemingly sympathetic toward the patients. He speaks in a quiet, measured voice and tends to listen carefully, giving people the impression that he understands them. Compared with the cruel and chaotic environment around him, Thredson initially seems safe and trustworthy. However, this calm exterior hides a deeply disturbed and manipulative personality. Thredson is highly observant and understands how to identify people's fears and weaknesses. Rather than relying on obvious intimidation, he gains control by earning trust. He is patient, calculating, charming, and extremely good at presenting himself as someone who wants to help. His intelligence makes him particularly dangerous because he is capable of carefully maintaining his respectable image while concealing his true nature. As Bloody Face, his personality becomes much darker. He is violent, obsessive, possessive, controlling, and psychologically unstable. His behavior is strongly connected to his traumatic childhood and his abandonment by his mother. He develops a disturbing obsession with motherhood and attempts to recreate the maternal relationship he believes he was denied. Although his past helps explain some of his psychological problems, it does not excuse his actions. Physically, Thredson has a handsome but serious appearance. He has an angular face, defined jaw, prominent cheekbones, dark brown hair, and intense eyes. His neatly styled hair and conservative glasses contribute to his intelligent, academic appearance. He usually wears formal suits, dress shirts, ties, and professional clothing appropriate for a psychiatrist in the 1960s. His body language is controlled and deliberate. He generally stands upright, moves calmly, and maintains steady eye contact when speaking. He rarely appears nervous or openly aggressive. His quiet voice and composed manner make him seem reassuring, which becomes disturbing once his true identity is revealed. The most important aspect of Thredson is the contrast between his appearance and his reality. He does not look like a stereotypical monster. He looks like an educated, respectable doctor—someone people would naturally trust. His intelligence, politeness, glasses, neat clothing, calm voice, and professional demeanor all help him hide what he really is. His greatest weapon is not physical strength, but his ability to make people believe he is safe.

Grace is a young patient at Briarcliff who becomes close to Kit. She is intelligent, caring, and wants to escape the asylum.

Kit is a young man accused of being the serial killer known as “Bloody Face.” He is sent to Briarcliff even though he claims he is innocent.

Lana is a brave and ambitious journalist. She goes to Briarcliff to investigate the asylum and expose its secrets.

Sister Jude is the strict head of Briarcliff Manor. She believes she is doing the right thing, but she can be cruel and controlling.

Sister Mary Eunice is a kind and innocent nun. After becoming possessed, her personality changes and she becomes dangerous.

Dr. Arden is a strange and cruel doctor at Briarcliff. He secretly performs disturbing experiments on people.