David is a young crime fiction writer working in 1920s Barcelona who grew up in extreme poverty. After finding commercial success with a penny dreadful series written under the pseudonym Ignatius B. Samson, he moves into a long-abandoned Gothic tower house to work from dusk until dawn. He suffers from severe headaches and harbors a deep, unrequited affection for his mentor's assistant.

Cristina is a pale, articulate young woman who works alongside her father for the Vidal family. She maintains a polite but reserved distance from David despite his obvious affection. Her life decisions are heavily influenced by a profound sense of obligation to Pedro for his continuous financial support.

Andreas is a mysterious French publisher associated with Éditions de la Lumière. He presents himself as an affluent, enigmatic figure with a distinct interest in David's specific writing talents. He makes an offer of 100,000 francs for David to write scripture for a new religion.

Pedro is the handsome, wealthy star writer and co-owner of the Voice of Industry newspaper. He takes David under his wing early on, providing him with a job after a family tragedy. Though successful socially and financially, he struggles immensely with his own literary output and relies heavily on his assistants.

Diego is a former lawyer whose old documents and belongings remain hidden in the tower house. Following the tragic drowning of his young son, he abandoned his legal career to become a writer and became heavily involved in local spiritualist circles.

Isabella is a passionate 17-year-old aspiring writer who greatly admires David's early crime fiction. She eagerly seeks his mentorship and offers to work as his assistant for free to improve her craft. She is determined, outspoken, and unafraid to challenge David's solitary habits.

Sempere is a kindly, aging bookseller who operates Sempere & Sons. He acts as a surrogate father figure to David during the boy's turbulent youth. He possesses a deep reverence for the printed word and serves as the guide to a secret, subterranean library.

Victor is a police inspector in Barcelona who previously interacted with David during the writer's time working the crime beat. He is sharp, observant, and views the city's various criminal occurrences with a highly skeptical eye.

Don Basilio is the deputy editor at the Voice of Industry newspaper. He is a demanding, no-nonsense newspaperman who provides David with his first professional writing assignment.

Barrido is a ruthless partner in the Barrido and Escobillas publishing house. He demands high-volume, sensationalistic penny dreadfuls from his writers and cares little for their physical or mental well-being.

Escobillas operates a publishing firm focused on cheap crime fiction. Like his partner, he prioritizes profit over quality and actively threatens legal action to enforce strict, demanding deadlines on his authors.

Isaac serves as the keeper of the Cemetery of Forgotten Books. He explains the strict rules of the labyrinth to new visitors and guards the massive, secret collection of discarded literature.

Manuel works as a chauffeur for the wealthy Vidal family. He relies on his position to support his daughter Cristina, establishing a deep sense of loyalty to his employer that influences his daughter's choices.

Pep works as an assistant to Pedro Vidal, helping manage the author's daily affairs and delivering messages among Pedro's social circle.

Dr. Trias is a physician in Barcelona who runs medical tests on David. He delivers a grim prognosis regarding an inoperable brain tumor, setting the story's main conflict into motion.

Alicia is the widow of Diego Marlasca, the lawyer who previously occupied David's home. She carries deep grief over the tragic loss of her young son in a backyard pool accident and remains suspicious about the true nature of her husband's death.

Ricardo is a former detective who investigated the suspicious drowning of Diego Marlasca 25 years earlier. His pursuit of the case led to his dismissal from the police force, leaving him highly cynical and armed.

Irene is a famous actress from David's youth who associated closely with spiritualists. Her past connections to the occult and her relationship with the previous owner make her a figure of interest in the history of the tower house.

Jaco is a hoodlum who involves himself in the occult practices of early 20th-century Barcelona, working alongside his partner to conduct supernatural sessions for grieving clients.

Damián is a spiritualist who previously conducted seances with Irene and Jaco. He caters to individuals seeking connection with the supernatural, though he maintains a highly practical view of his own trade.

Sebastian is a practicing lawyer and the son of Diego Marlasca's former business partner. He retains historical knowledge of his father's firm and its past associates, answering David's questions about the tower house's history.

Don Odon operates a store in Barcelona and cares deeply for his daughter Isabella. Despite her dramatic claims that he threatened her with a shotgun, he is actually a practical and supportive parent happy to see her find gainful employment.

Dr. Sanjuan is a physician working at a sanatorium north of Barcelona. He oversees the care of patients experiencing severe psychological distress and encourages visitors to aid in their recovery.

Marcos is a rough police deputy working under Inspector Grandes. He acts as the muscle for the department, fetching suspects for interrogation without explanation.

Castelo is a police deputy who assists Inspector Grandes in his investigations. He frequently works alongside Marcos to intimidate and transport suspects across Barcelona.