Father Brown is a short, unassuming English Catholic priest from Essex who wears shapeless clothes. He possesses a sharp, analytical mind and serves as an amateur detective. Because his priestly duties require him to hear confessions, he has developed a deep understanding of human psychology, morality, and the capacity for evil. He relies on this spiritual intuition and his acute observation of human behavior to solve mysteries that baffle traditional police forces.

Flambeau is a towering, infamous French thief known for his extraordinary physical strength and his elaborate, theatrical crimes. He views thievery as an art form and often styles his robberies around specific themes or holidays. Despite his criminal profession, he possesses a certain code of honor and an intellectual curiosity that draws him into frequent contact with Father Brown.

Valentin is the renowned chief of the Paris police. He is a straightforward, highly logical investigator who believes he can catch criminals by anticipating their unorthodox thought patterns. He holds fiercely anti-religious and anti-clerical views, viewing the Catholic Church and religious superstition as inherently irrational and dangerous to modern society.

Wilfred is an Anglican Reverend living in the village of Bohun Beacon. Coming from a once-prestigious but currently dwindling aristocratic family, he takes his faith extremely seriously. He maintains a rigid, uncompromising moral code and constantly clashes with those who display vulgar or blasphemous behavior in his presence.

St. Clare is a deceased British general celebrated throughout England as a tragic military hero. He is famous for leading a doomed military charge against Brazilian forces in the 19th century, an event that ended with his hanging. His public legacy serves as a source of national pride and imperialist propaganda.

Brayne is a wealthy American millionaire with a strong interest in progressive ideas and world religions. Though historically a skeptic, he begins exploring the Catholic faith, which causes severe friction between him and his strictly atheistic host during a dinner gathering.

O'Brien is an Irish-born officer serving in the French Foreign Legion. He attends Aristide Valentin's dinner party, where he seeks a private moment to propose marriage to Lady Margaret Graham.

The Duchess of St. Michel and the daughter of Lord and Lady Galloway. She finds herself cornered in a garden by Commandant O'Brien, who aggressively seeks her hand in marriage.

The English Ambassador to France. He is highly protective of his daughter, Lady Margaret Graham, and becomes visibly agitated when he realizes she is missing from the main drawing room.

A young woman who lives with her father, Colonel Adams. She receives a highly valuable set of diamonds called the Flying Stars from her godfather for Christmas, which quickly become the target of a local theft.

A journalist and outspoken socialist who is romantically involved with Ruby Adams. His vocal political opinions make him an easy target for suspicion among the wealthier members of Ruby's family.

A young woman who works in a shop and finds herself the object of affection from multiple men. She feels deeply uneasy about her past interactions with two specific suitors from her hometown and attempts to avoid them by setting high financial standards for marriage.

A Scottish man deeply in love with Laura Hope. When he learns that she is being targeted and threatened by figures from her past, he immediately seeks outside help to protect her and secure their future together.

A wealthy inventor who has made a fortune building mechanical household servants. He returns to London to win Laura Hope's hand in marriage but begins receiving terrifying death threats from a romantic rival.

A highly reclusive man who spends his time taking long, solitary walks through the countryside. He holds an obsessive desire to marry Laura Hope and sends violent, threatening messages to anyone who attempts to court her.

A Scottish peasant who serves as the attendant and eventual heir to Lord Glengyle. He appears to be deaf and mentally disabled, leading local investigators to misunderstand his strange hoarding behaviors following his master's death.

An old friend of Hercule Flambeau who works as a romantic poet. He suffers from a severe opium addiction and holds a deep, unsettling obsession with Eastern mysticism and exotic artifacts, which fill his home.

Leonard Quinton's attending physician. He is a staunch atheist who believes strictly in science and logic, rejecting traditional morality in favor of pursuing pure, rational happiness. He harbors deep feelings for his patient's wife.

A prominent French aristocrat residing in Norfolk. He spent years living in Vienna and traveling the world to escape the fallout of a scandalous affair in Italy that resulted in a man's death. He invites Hercule Flambeau to visit his estate.

A young Italian man seeking violent retribution against Prince Saradine. He claims the prince ruined his family by having an affair with his mother and murdering his father when Antonelli was only an infant.

A vulgar, atheistic aristocrat who openly mocks religion and engages in highly immoral behavior. His blatant disrespect for faith severely strains his relationship with his deeply religious younger brother.

A wealthy heiress who uses her fortune to support progressive causes. She becomes heavily involved in a new sun-worshiping religion, leading her to adopt radical beliefs about physical health and the power of levitation.

The charismatic priest of a modern pagan religion centered around the sun god Apollo. He preaches that human beings are inherently virtuous and can achieve physical perfection through sheer faith, drawing wealthy followers like Pauline Stacey into his inner circle.

A highly beloved Scottish comic known across British society for his boundless cheerfulness. He built his entire public reputation on his unfailingly positive demeanor and his status as a recovering alcoholic.

Sir Aaron Armstrong's loyal Irish secretary. He is deeply protective of the Armstrong family, particularly Alice, and fiercely attempts to control the narrative surrounding his employer's affairs.

The young daughter of Sir Aaron Armstrong. She finds herself trapped in a highly stressful domestic situation involving her father's declining state and her forbidden romance with his secretary.