Agnes Aubert is a 35-year-old widow who runs a struggling cat shelter in Montréal called Les Amis des Chats. Her life is governed by checklists and routines, which she relies on to impose order and manage the grief of losing her husband. Desperate to find a new location for her 52 feline charges before winter, she rents a suspiciously affordable shop on Rue des Hirondelles.

Havelock Renard is an infamous dark magician known publicly as the Witch King, a figure feared for his rumored role in a near-apocalyptic event. However, his private reality contrasts sharply with his fearsome reputation, as he is an isolated, bookish scholar who suffers from a severe allergy to cats. He uses the basement of the Rue des Hirondelles shop as a clandestine workshop for his magical experiments.

Valérie Renard is a powerful, charismatic magician and Havelock's twin sister. She leads a faction of followers who believe magic should be practiced openly and without restraint. She actively hunts for Havelock to seize a mythical magical Artefact she believes he possesses, caring little for the non-magical lives caught in her path.

Élise is Agnes's fiercely pragmatic and resourceful younger sister. She acts as Agnes's anchor to the practical world, constantly looking out for her well-being and assisting with the physical demands of moving the cat shelter. She is deeply protective, preferring ordinary safety over magical complications.

Yannick Abrams is an earnest, anxious young man who acts as the leasing agent for the Rue des Hirondelles shop. He is Havelock's loyal apprentice, having sought refuge with the magician after his own family rejected him for possessing magic. He serves as an awkward bridge between the city's hidden magical underbelly and Agnes's mundane business.

Laurent Rouzet is a handsome and inquisitive police detective investigating the absentee owner of the Rue des Hirondelles shop. He presents a friendly, neighborly demeanor while attempting to gather information about potential illegal magical activity occurring on the premises.

Mina is a dedicated volunteer who helps Agnes manage the daily operations of Les Amis des Chats. She assists in the massive undertaking of moving the cats and adapting to their unusual new environment.

Gabriel is Élise's husband and a local politician preparing for an upcoming election. His political career makes him highly sensitive to public scandals or unusual incidents involving his family.

Robin is Agnes's late husband who died two years prior to the events of the story from a rare heart condition. He co-founded Les Amis des Chats with Agnes and shared a special bond with the shelter's most difficult feline resident.

His Majesty is a large, tyrannical, semi-feral black cat who resides at the shelter. He was especially fond of Agnes's late husband, Robin, and actively resists typical attempts at domestication, ruling the other cats with an iron paw.

Oksana owns the bookstore neighboring the Rue des Hirondelles shop. She is highly observant of the neighborhood's secretive activities and provides cryptic warnings about the shop's history.

Dr. Noémie Para is a veterinarian who treats the animals at Les Amis des Chats. She is pragmatic and focuses on the physical well-being of the cats, diagnosing their stress after the shelter's sudden environmental changes.

Roger Fairwood is a wealthy shipping magnate who becomes the shelter's first customer at its opulent second location. He adopts an elderly cat and pays a generous fee, later inadvertently causing a stir by spreading rumors about the animals.

Banshee is a voiceless tabby cat who belongs to Agnes's personal collection of felines. She provides a quiet, comforting presence in contrast to the aggressive nature of His Majesty, often seeking out warm spots near magical energy.

M. Levasseur is a landlord who initially sympathizes with Agnes's difficult situation before abruptly changing his mind.