Stephen is a young man from London who has recently been released from a Borstal Institution after serving two years for grievous bodily harm. Working with the Borstal Society to find legitimate employment, he arrives at the isolated Tithe Hall with a forged recommendation letter. He is observant and hyper-aware of social dynamics, using his working-class background to operate within the strict hierarchy of the Edwardian estate. His primary goal is to maintain stable employment and avoid returning to prison, though he quickly becomes the prime suspect when a murder occurs.

Miss Decima is the elderly, sharp-tongued great-aunt of the Viscount, confined to the isolated Nursery wing of Tithe Hall. Once a brilliant scientific mind, she sacrificed her career to care for her father and harbors deep bitterness toward her family. She rejects the Viscount's apocalyptic theories about Halley's Comet, preferring rigorous astronomical observation and evidence-based logic. When a murder occurs, she seizes the opportunity to exercise her suppressed intellect by launching her own investigation.

Mr. Stokes is the Head Butler at Tithe Hall, commanding absolute authority over the downstairs staff. He embodies the ideal Edwardian servant, maintaining a placid exterior while enforcing strict rules about invisibility and decorum. He manages the frantic demands of the Viscount with practiced efficiency, though he bristles under the family's harsh treatment. He surprises Stephen by agreeing to hire him despite the lockdown protocols.

Temperance is a young ladies' maid working at Tithe Hall who initially appears timid and easily overwhelmed by the estate's harsh environment. Hailing from London, she forms a quick connection with Stephen over their shared working-class backgrounds. She possesses a sharp mind and is an avid reader of detective fiction, skills she brings to bear when she joins Miss Decima's unofficial murder investigation.

The Viscount is the arrogant and wealthy master of Tithe Hall who claims to be a leading scientific mind. Convinced that the cyanogen gas in Halley's Comet will destroy all life on Earth, he imposes a tyrannical lockdown on the estate to ensure his family survives to rule the post-apocalyptic world. He treats his staff with contempt and uses his wealth and aristocratic title to enforce his narcissistic delusions upon everyone around him.

Edwin is a Member of Parliament and the Viscount's cousin, who expects to inherit Tithe Hall. He arrives at the estate anticipating a serious discussion about the family will, only to be trapped in his cousin's apocalyptic lockdown. He is a pragmatic, self-serving politician who prioritizes the preservation of the family's public reputation above all else, swiftly taking control of the household after the murder to suppress any potential scandal.

Inspector Jarvis is a detective from Scotland Yard dispatched to investigate the murder at Tithe Hall. He is theatrical, condescending, and heavily reliant on pseudoscientific theories, such as phrenology, rather than physical evidence. He immediately fixates on the household staff as suspects, using his position of authority to construct elaborate, prejudiced narratives that align with his worldview.

Lettice is the Viscount's cousin, presenting herself as a demure widow concerned only with the welfare of her grandson. Behind her respectable mourning attire and constant demands for tea, she is a shrewd and opportunistic woman desperate for financial security. She uses the chaotic lockdown at Tithe Hall to secretly advance her own interests, exploiting the secrets of others to secure tuition money for her grandson.

Gilbert is Lettice's young grandson, brought to Tithe Hall amidst the comet panic. He frequently requests food and attention, adding to the chaotic environment for the servants. He is morbidly curious about the murder and produces disturbing drawings depicting violence against the other family members.

Jolyon is a former Rear Admiral in the British Navy and a cousin of the Viscount. Heavily in debt and struggling with an alcohol dependency, he is primarily concerned with staving off boredom during the estate's lockdown. He treats the household staff as his personal valets and uses the chaotic environment to covertly indulge his drinking habit.

Lowen is the first footman at Tithe Hall, a position he guards with intense insecurity. Noticeably shorter than Stephen, he wears heeled shoes and resents the new arrival, viewing Stephen as a direct threat to his wages and status. He is hostile and aggressive, actively attempting to make Stephen's work miserable while currying favor with the aristocratic guests.

Professor Müller is a German scientist invited to Tithe Hall to validate the Viscount's apocalyptic theories. He meticulously documents the estate's lockdown with his camera, frequently blocking corridors and irritating the family. Despite his academic credentials, he exhibits highly suspicious behavior following the murder and harbors embarrassing personal secrets that make him vulnerable to extortion.

Mrs. Pearce is the housekeeper at Tithe Hall, responsible for managing the female staff and maintaining order below stairs. She is a pragmatic woman who understands the precarious nature of domestic employment and attempts to keep the maids focused despite their superstitions about ghosts and the comet.

Merryn is a young maid at Tithe Hall who is highly susceptible to the superstitious rumors circulating among the staff. She becomes convinced that the estate is haunted by the previous master, frequently interpreting the strange noises of the locked-down house as supernatural activity.

Lawrence Welt is the late father of the current Viscount, having died twenty years prior from a crossbow bolt to the eye. His mysterious death casts a long shadow over Tithe Hall, generating fearful gossip among the staff and serving as a macabre blueprint for his son's eventual murder.

Nan is Stephen's late grandmother, whose care motivated his initial descent into crime. Though she died while he was incarcerated, her memory serves as his moral compass and drives his intense need for redemption and stability.

Isabella Welt is Miss Decima's late sister who died giving birth to the Viscount. Her estrangement from Decima prior to her death is a source of profound regret, influencing Decima's determination to uncover the truth behind her son's murder.