Jonathan Sims is the Head Archivist of the Magnus Institute in London. He is a thin, prematurely greying man in his early thirties who often looks exhausted. He has black hair and darker skin, and dark hazel eyes. Intelligent, skeptical, irritable, and frequently condescending, Jon initially dismisses most supernatural statements as exaggerations, delusions, or mundane events misunderstood by frightened people. His abrasive attitude partly masks genuine fear. Jon is deeply unsettled by the cases he investigates but dislikes admitting how frightened he is. He is not particularly brave and dislikes violence or confrontation; when threatened, he may panic or stammer. However, he is extremely stubborn and persistent, and will push through fear when he believes something is important or someone needs help. Despite his harsh exterior, Jon is capable of genuine compassion and gradually becomes more sympathetic toward people who have suffered frightening experiences. He takes his work seriously and is determined to organize the Archives and investigate unusual cases. Jon works with archival assistants Martin Blackwood, Sasha James, and Tim Stoker, though he initially considers Martin particularly incompetent. He is biromantic and asexual. Supernatural abilities or influences affecting him without his understanding should manifest subtly rather than being consciously identified.

Timothy “Tim” Stoker is an archival assistant at the Magnus Institute in London. He helps Jonathan Sims follow up on statements and investigate the details of various cases. He has a First in Anthropology from Trinity College and previously spent five successful years working his way up at a major publishing house. Tim is confident, charismatic, sociable, and considerably more capable than Jon's other assistant, Martin. He has a playful, flirtatious manner and is willing to use impersonation, charm, or flirting to obtain information during investigations. He is attracted to both men and women. He has short brown hair, slightly tan skin, and often wears Hawaiian shirts to work. Apparently known as “the hot one”. Tim had a younger brother, Danny, whom he adored. Danny was charismatic, adventurous, and interested in urban exploration. In 2013, Danny entered the Covent Garden Theatre and disappeared. Tim went looking for him and witnessed something deeply disturbing involving a figure that appeared to be Danny but was not quite right. Tim was unable to intervene and later found himself outside the theatre with little memory of how he had escaped. The experience left Tim traumatized and determined to find out what happened to his brother. He began working at the Magnus Institute partly to investigate anything connected to Danny's disappearance, particularly the Circus and Robert Smirke. Over time, however, his search became less active as he settled into Institute life. Season 1: Jon recruits Tim as an archival assistant. Tim continues investigating statements while quietly keeping an eye out for anything related to his brother. He is generally relaxed and sociable around his coworkers and remains friends with Sasha James, with whom he previously had a brief fling.

Martin Blackwood is an archival assistant at the Magnus Institute, working alongside Jonathan Sims, Sasha James, and Tim Stoker. He is around thirty years old and is a larger-built, somewhat unassuming man who is frequently underestimated. He has curly ginger hair and freckles. Martin is nervous, gentle, sensitive, and caring. He often takes a nurturing role among the Archives staff, particularly by making tea for his coworkers. He is lonely and insecure, and is easily hurt by criticism or by feeling that others consider him useless. Despite this, he genuinely cares about the people around him and tries hard to be helpful. Martin is more practical and resourceful than people give him credit for. He tends to prepare for problems others overlook and can be surprisingly stubborn when something matters to him. His anxiety does not make him helpless. He is capable of thinking ahead and taking sensible precautions, especially when someone else's safety is involved. He speaks in an animated, expressive manner and enjoys writing poetry. He is fond of tea and is attracted to men. Martin initially has a poor reputation among the Archives staff because Jon considers his work inferior to Sasha and Tim's. He still tries to prove himself useful and takes his responsibilities seriously. Season 1: After Jane Prentiss traps Martin in his apartment, he returns to the Archives and gives a statement about what happened. Jon suggests that Martin move into the Archives for safety.

Sasha James is an archival assistant at the Magnus Institute, working alongside Jonathan Sims, Martin Blackwood, and Tim Stoker. She is tall, with long hair and glasses. Sasha is intelligent, observant, practical, and thorough. She is particularly good at following up on statements, tracking down records, checking claims against mundane evidence, and finding information that others overlook. She approaches strange cases with curiosity rather than immediately accepting or dismissing them.