Ambrosio is the celebrated head of the Capuchin monastery in Madrid. Abandoned on the monastery steps as a child, he rises to a position of immense public reverence due to his strict adherence to monastic vows and his charismatic preaching. While the public views him as a flawless saint, he privately harbors deep pride and vanity regarding his own virtue. His strict, isolated upbringing leaves him ill-prepared when he finally confronts temptation.

Matilda is a beautiful noblewoman who initially disguises herself as a male monk named Rosario to infiltrate the Capuchin monastery. Driven by a passionate obsession with Ambrosio, she uses her intellect, charisma, and hidden knowledge to systematically dismantle his moral defenses. She holds radical views for her era, advocating for personal liberty, free love, and the rejection of societal constraints. Her influence pulls Ambrosio away from his strict religious vows.

Antonia is a fifteen-year-old girl who recently moved to Madrid with her mother. Raised in strict isolation to protect her virtue, she possesses an extreme innocence that leaves her entirely ignorant of the world and the intentions of others. Her striking physical beauty quickly catches the attention of the city's noblemen and religious figures alike. She struggles to understand the complex social dynamics of her new city.

Agnes is a noblewoman forced to join the Convent of St. Clare due to a vow her mother made before her birth. Intelligent and rational, she frequently mocks the superstitions of the convent and longs for a life outside its walls. Her attempts to escape her constrained existence set her on a collision course with the strict rules of her religious order.

Don Lorenzo is a wealthy Spanish nobleman who embodies traditional aristocratic honor and youthful romantic passion. He recently returned to Madrid to visit his sister at the convent, but his focus shifts when he falls instantly in love with the commoner Antonia. He is assertive, decisive, and willing to cross class boundaries to pursue his romantic interests. He maintains a skeptical view of the city's religious fervor.

Don Raymond, also known as the Marquis de las Cisternas, is a well-traveled Spanish nobleman. He spent time touring Europe under an assumed name to observe common society, a journey that led to numerous dangerous adventures. He goes to extreme lengths, including adopting disguises and attempting elaborate elopements, to rescue Agnes from her family and the convent.

The Prioress is the authoritarian head of the Convent of St. Clare. She prioritizes the wealth, prestige, and social power of her convent above genuine religious faith, actively recruiting beautiful noblewomen to increase the institution's standing. Behind a facade of holy discipline, she exercises cruel and sadistic control over the women in her charge, punishing rebellion with extreme severity.

Theodore is the youthful, handsome valet to Don Raymond. Taken into the nobleman's service after a traumatic incident in Germany, Theodore proves fiercely loyal and highly capable. He acts as an essential operative for both Don Raymond and Don Lorenzo, executing stratagems and gathering information that the noblemen cannot obtain directly. He is also a talented singer and poet.

Elvira is the widow of a nobleman, originally born to a common shoemaker. Her marriage brought her immense suffering at the hands of her husband's aristocratic relatives, making her deeply cynical about society and cross-class relationships. She is fiercely protective of her daughter, going to extreme measures to shelter her from the corruption and moral dangers of Madrid.

Mother St. Ursula is a highly respected nun within the Convent of St. Clare. Unlike the Prioress, she maintains genuine compassion for her fellow sisters and actively opposes the cruel punishments meted out within the convent walls. She serves as a critical ally to those seeking to expose the corruption of the institution.

The Bleeding Nun is a violent, spectral figure said to haunt a German castle every five years. According to legend, she was a nun who broke her vows, engaged in debauchery, and murdered her lover before perishing. Her ghostly presence drastically disrupts Don Raymond's plans when he unwittingly involves her in his romantic schemes.

The Stranger is a mysterious, majestic sorcerer who possesses profound knowledge of the supernatural world. Carrying an aura of dark power, he wields the magical authority necessary to command spirits and break supernatural curses.

Satan appears as an entity of immense supernatural power, initially manifesting in the form of a flawless, beautiful youth rather than a terrifying monster. He preys on the pride and vanity of mortals, using attractive illusions and magical artifacts to encourage their descent into corruption.

Antonia's Aunt is a practical woman who helps her sister Elvira and her niece adapt to their new life in Madrid. She acts as a chaperone and conversationalist, eagerly detailing her family's difficult history to the curious noblemen they encounter at church.