Morrigan is an 11-year-old girl living in the Republic who believes she is a cursed child, doomed to die at midnight on her 12th birthday. Having grown up neglected and blamed for every misfortune in her hometown of Jackalfax, she expects nothing but a short, isolated life. When she receives unexpected bids for her future, her path shifts dramatically, sending her to the magical Free State where she becomes a candidate for the elite Wundrous Society.

Jupiter is the eccentric, optimistic owner of Hotel Deucalion in the Free State of Nevermoor. Serving as a sponsor for the Wundrous Society, he selects candidates to undergo rigorous trials for admission. He wears bright clothing, possesses a shocking ginger beard, and maintains an upbeat demeanor that sharply contrasts with the gloomy environment Morrigan leaves behind.

Hawthorne is a fellow candidate undergoing the Wundrous Trials. Playful and fiercely opposed to bullies, he quickly becomes Morrigan's first genuine friend in Nevermoor. Unlike others who evaluate candidates based on their utility, Hawthorne offers his companionship freely and routinely involves Morrigan in mischievous activities.

Ezra Squall is a wealthy industrialist who controls Squall Industries, the primary producer of energy in the Republic. He is physically represented by a sharply dressed, deathly pale man with spidery hands who initially introduces himself as an assistant. He extends a highly unusual offer to Morrigan, serving as a mysterious and persistent figure keenly interested in her potential.

Cadence is a highly confident and slightly antagonistic candidate competing in the Wundrous Trials. Sponsored by Baz Charlton, she possesses a unique ability to command attention and influence others. Her interactions with Morrigan are tense, though they develop a cautious mutual respect when their paths cross during the trials.

Corvus is Morrigan's father and a prominent politician in the Republic town of Jackalfax. He cares deeply about his political reputation and public standing, viewing his daughter's cursed status as an irritating inconvenience. He shows little emotional warmth and prioritizes his career over his family's well-being.

Fenestra is a large, talking Magnificat who serves as the head of housekeeping at Hotel Deucalion. Formerly a cage fighter, she is fierce, territorial, and highly capable in a physical conflict. Despite her abrasive exterior and constant complaints, she proves to be a reliable protector for those living in the hotel.

Jack is Jupiter's nephew who returns to Hotel Deucalion early from school. He initially clashes with Morrigan, viewing her presence in the hotel with suspicion and doubting her capabilities as a Wundrous Society candidate. He has strong opinions about local holiday traditions.

Noelle is a highly competitive and cruel candidate sponsored by Baz Charlton. She takes pleasure in bullying others and aggressively looks down on Morrigan for being an undocumented resident of the Free State.

Baz is a Wundrous Society sponsor and a colleague of Jupiter North. Sponsoring eight candidates in the current trials, he heavily involves himself in the politics of the society and openly questions Jupiter's decision to support an unknown girl like Morrigan.

Dame Chanda is a glamorous singer and permanent resident of Hotel Deucalion. She takes an immediate liking to Morrigan, offering her fashion advice, social support, and historical information about Nevermoor.

Inspector Flintlock is a strict officer of the Free State Police. He is determined to track down undocumented individuals and repeatedly attempts to verify Morrigan's legal status in the Free State, posing a constant bureaucratic threat to her safety.

Anah is a quiet candidate participating in the Wundrous Trials. She lives in a convent and dresses plainly, making her an easy target for bullies until Morrigan steps in to defend her.