Lenore is a 30-year-old woman trapped in a meticulously managed but emotionally sterile 10-year marriage to a wealthy steel industrialist. Haunted by the traumatic death of her parents and a harsh upbringing, she finds a superficial sense of control in curating her household's social standing. Her carefully constructed life begins to unravel when she starts experiencing vivid dreams and a mysterious illness.

Carmilla is a mysterious, beautiful woman who survives a carriage crash near the Crowthers' new country estate, Nethershaw. Placed in Lenore's care, she is evasive about her family and destination. Her unsettling presence and unapologetic appetites act as a disruptive force in the household, challenging the restrictive social conventions of Victorian society.

Henry is an ambitious, new-money steel industrialist who owns the Ajax Works factory in Sheffield. He views his marriage to an aristocratic woman as a strategic business acquisition and desires to cement his status among the landed gentry. He projects a veneer of gentlemanly charm, but his ruthless ambition dictates both his domestic behavior and his exploitative business practices.

Cora is Lenore's pretty, wealthy, and conventionally feminine friend. She moves through society with an unthinking confidence that starkly contrasts with Lenore's deep anxieties. Invited by Henry to stay at Nethershaw, her close proximity to him quickly stirs tension and suspicion within the household.

Aunt Daphne is Lenore's deceased relative who raised her following the traumatic deaths of Lenore's parents. She ran an austere, mausoleum-like household and subjected her niece to severe emotional abuse. Her harsh tutelage conditioned Lenore to view her own needs as a burden.

Molly is Lenore's maid. She assists with the daily operations of the household but begins to act strangely after Carmilla arrives, exhibiting trance-like behaviors and uncharacteristic appetites.

Dr. Bartolomé is a local physician called to Nethershaw to treat Carmilla. He insists she is too unwell to travel due to shock and a weak heart, cementing her stay at the estate.

Laurence Gibson is a journalist investigating the industrial relations and safety conditions at Henry's Ajax Works factory. He attempts to question Lenore about compensation policies before Henry intervenes.

Detective Inspector Lacey is a local police officer tasked with investigating grim incidents around the Derbyshire moors and Hathersage. He is observant and sympathetic, offering Lenore an official outlet during her domestic crises.

Dr. Foxfield is a physician summoned to Nethershaw to evaluate Lenore's sanity. He holds typical Victorian assumptions about female fragility and hysteria, making him susceptible to manipulation.