Beatrice is a wealthy noblewoman who lives in her father's castle. Though she presents an image of virtuous innocence, she possesses a strong will and deeply passionate emotions. Forced by her father to accept a sudden betrothal to Alonzo, she feels trapped when she falls instantly in love with Alsemero. Determined to follow her heart, she seeks ways to exercise agency and alter her destiny within the strict confines of her patriarchal society.

De Flores is a servant in Vermandero's castle who harbors an intense, obsessive infatuation with Beatrice. Born a gentleman, his life circumstances forced him into servitude, leaving him with a complicated social standing and bitter pride. He is highly self-aware of his ugly physical appearance and the disgust it inspires in his master's daughter, yet he remains entirely undeterred in his pursuit of her attention.

Alsemero is a respectable nobleman from Valencia who stops in Alicante during his travels. A man of science and strong moral principles, he is typically not prone to impulsive decisions until he spots Beatrice. Smitten by her beauty, he immediately halts his travel plans and seeks to court her, viewing their union as blessed by divine providence.

Vermandero is a prominent Spanish nobleman and the master of the castle where much of the narrative unfolds. As a strict but respectable patriarch, he exerts total control over his household and his daughter's future. He values honor, duty, and beneficial alliances, having arranged Beatrice's swift marriage to a suitable gentleman.

Alonzo is a noble and honorable gentleman newly engaged to Beatrice. Completely unaware of his bride-to-be's sudden infatuation with another man, he remains optimistic about their upcoming wedding. He tends to view the world and the people around him with a trusting and naive perspective.

Tomazo is Alonzo's highly observant and protective brother. Unlike Alonzo, Tomazo quickly senses that Beatrice's attitude toward the upcoming marriage is unusually cold and indifferent. He tries to warn his brother about these suspicious signs, though his concerns are dismissed.

Diaphanta is Beatrice's waiting-woman and loyal attendant within the castle. She facilitates private interactions between her mistress and Alsemero, serving as a trusted confidant in Beatrice's romantic pursuits.

Jasperino is Alsemero's loyal friend and traveling companion. He is greatly surprised when Alsemero suddenly abandons their travel plans for a newly discovered romance, as he has never known his friend to be distracted by love.

Alibius is an older doctor who manages a mental asylum, keeping patients for public entertainment. He is deeply insecure about his age difference with his beautiful young wife, Isabella, and goes to extreme lengths to isolate her from any potential temptation.

Isabella is Alibius's young, beautiful wife. Despite her husband's intense jealousy and his decision to lock her inside the asylum away from the public, she maintains her faithfulness. Her forced confinement causes her to resent her lack of freedom, and she attracts the attention of several men attempting to woo her.

Lollio is the trusted servant in Alibius's asylum. Tasked with managing the patients and serving as Isabella's warden, he takes advantage of his master's absence to make his own advances toward Isabella.

Antonio is a gentleman who masquerades as a fool (a "changeling") in Alibius's asylum. He willingly submits to the degrading treatment of the asylum solely to gain access to the isolated Isabella and declare his love for her.

Franciscus is a poet who infiltrates the asylum by pretending to be a madman suffering from lovesickness. Like Antonio, he uses his lunatic disguise as a method to slip past Alibius's defenses and court Isabella.