Alibius

Alibius is a jealous old doctor who is in charge of a private lunatic asylum. He is married to Isabella, a woman much younger than himself, and he is worried that when he is away another man may usurp his position. He therefore instructs his servant Lollio to prevent any of the visitors to the asylum, who may include young nobleman who come to gawk at the inmates, from seeing Isabella.

Alsemero

Alsemero is a nobleman from Valencia who falls in love with Beatrice. He immediately postpones his voyage to Malta to declare his love for her. Alsemero is an honorable man. When he finds out that Beatrice is betrothed to Alonzo but would sooner marry him, Alsemero, he wants to challenge Alonzo to a duel. But Beatrice refuses to allow this. When Jasperino informs him that he and Diaphanta have overheard suspicious conversations between De Flores and Beatrice, Alsemero gives her a potion that is supposed to reveal whether a woman is a virgin. Not a jealous man by nature, he does not want to think ill of his new bride and is relieved when she passes the test. When Beatrice is finally forced into confessing her crime to him, he is horrified and rejects her utterly.

Antonio

Antonio is the changeling, the counterfeit fool. He is a member of Vermandero's staff, but he gets permission to leave for a while, pretending that he is going on a trip to Bramata. In truth, he wants to gain access to Isabella, so he pretends to be a fool and is admitted to the lunatic asylum. After a while he casts his disguise aside and declares his love for Isabella. Unfortunately for Antonio (as well as for Franciscus), he happens to enter the asylum on the same day that Alonzo is murdered. When this fact transpires, Vermandero arrests him for murder. He is only spared the gallows when the truth comes out in the final scene.

Beatrice

Beatrice, also called Joanna, is the young, beautiful daughter of Vermandero. But behind her beauty lies an immature, selfish, cruel and cunning nature. When the plays begins, she is engaged to marry Alonzo, and it appears that she has some affection for him. But as soon as Alsemero declares his love for her, she switches her affections to the new man. Not wanting to be thwarted in her desires, and without a thought for the possible consequences, she employs De Flores, a man whom she loathes and despises, to murder Alonzo. But she completely misjudges De Flores. She thinks she can pay him for his services and get him to leave the country; instead, he demands sex from her. She is forced to submit to him, since he makes her realize that they are partners in crime and she cannot escape from him. But this creates another problem for her. Although she is now free to marry Alsemero, she cannot allow him to detect on their wedding night that she is not a virgin, so she employs Diaphanta to go to Alsemero's bed in her place. De Flores then efficiently disposes of Diaphanta in a house fire, before the truth can come out, and Beatrice decides that she is now in love with him. Her crimes catch up with her when Jasperino overhears incriminating conversations between her and De Flores and reports them to Alsemero. When challenged by her husband, she confesses her role in the murder, but omits the substitution of Diaphanta in the marriage bed. After being rejected by her husband, she is stabbed by De Flores. Wounded, she is shamed in front of her father, and finally admits the full truth to Alsemero just before she dies.

De Flores

De Flores is a servant of Vermandero, Beatrice's father. He has an ugly appearance, particularly the skin on his face. De Flores is known to most people as an honest man, and Vermandero thinks highly of him. But in fact De Flores has no ethical sense at all, and his besetting sin is his sexual obsession with Beatrice. He invents any little excuse to go and see her, even though she loathes him and insults him. He is ready to endure such humiliations simply to have a glimpse of her. De Flores is more experienced and worldly-wise than Beatrice, and when she hints to him that she would like to see Alonzo murdered, he at once sees how he can use the opportunity to blackmail her into sexual submission. After he has killed Alonzo, he ignores Beatrice's attempts to buy him off, insisting that he will only be satisfied by his sexual enjoyment of her. Having outwitted and outmaneuvered her, he has his desire. Then, when Beatrice is threatened by the fact that Diaphanta has not returned from Alsemero's bed, it is De Flores who thinks up a scheme to save her. De Flores is so efficient in planning and acting upon it that Beatrice convinces herself that he is a man worth loving, because he takes such good care of her. Although De Flores does have some moments when his conscience troubles him, when his crimes are discovered, he remains defiant. He kills himself and Beatrice so they can be together in hell.

Diaphanta

Diaphanta is Beatrice's maid who flirts with Jasperino. At Beatrice's request, she takes Beatrice's place in Alsemero's bed on the wedding night. Beatrice thinks Diaphanta is a little too eager to accept the assignment and wonders whether she really is a virgin. But she is satisfied when she gives Diaphanta the test for virginity prescribed in a medical book, and the maid passes it. But Diaphanta apparently enjoys her love-making with Alsemero since she fails to return at midnight, as she had promised. When the first streaks of dawn appear in the sky, De Flores sets fire to Diaphanta's chamber, to lure her home. When the alarm is sounded about the fire, Diaphanta rushes back to her chambers, where she meets her death in the flames, just as De Flores had intended.

Franciscus

Franciscus is an employee of Vermandero who gets a leave of absence. He uses it to disguise himself as a madman and enter the lunatic asylum, where his purpose is to declare his love for Isabella. For a while he acts like a madman, but then sends Isabella a love letter, which unfortunately for him is intercepted by Lollio. Franciscus is arrested along with Antonio on suspicion of the murder of Alonzo, and would have been hanged had the truth not come out.

Isabella

Isabella is the young wife of Alibius. She is attractive to men and her old husband fears that her affections may stray. Confined to a room where she may only meet the inmates of the lunatic asylum rather than the visitors, she finds herself subject to the unwanted romantic attentions of Antonio and Franciscus. She also has to fend off an attempted seduction by Lollio. Isabella's common sense and good judgment are contrasted with Beatrice's complete lack of those qualities.

Jasperino

Jasperino is Alsemero's friend. He expresses surprise at Alsemero's sudden change of plans after he falls in love with Beatrice, and decides that he will entertain himself by seducing Diaphanta, who seems more than willing to be seduced. Jasperino later reports to Alsemero that he and Diaphanta have overheard incriminating conversation between De Flores and Beatrice.

Lollio

Lollio is Alibius's servant. Alibius charges him with ensuring that none of the visitors to the lunatic asylum are allowed to see Isabella. Lollio, who wants to seduce Isabella himself, readily agrees. He introduces Franciscus and then Antonio to Isabella, not realizing that they are only pretending to be madman and fool, respectively. When Lollio tries to kiss Isabella, she rebuffs him severely, telling him that if he does not stop, she will get Antonio to cut his throat. Lollio then tries to set Antonio and Franciscus against each other by telling each man separately that Isabella is in love with them.

Pedro

Pedro is Antonio's friend who takes him to the lunatic asylum.

Alonzo de Piracquo

Alonzo de Piracquo is a nobleman who when the play begins is engaged to marry Beatrice. Beatrice's father thinks very highly of him and is pleased that he is going to he his son-in-law. But Beatrice quickly loses interest in Alonzo when she meets Alsemero. Alonzo's brother Tomazo warns him not to marry Beatrice but he does not listen. He is murdered by De Flores as De Flores shows him around Vermandero's castle.

Tomazo de Piracquo

Tomazo de Piracquo is Alonzo's brother. He sees that Beatrice does not love Alonzo, and advises him not to marry her. After the murder of Alonzo, Tomazo comes to Vermandero's castle, seeking revenge, but he does not know the identity of the murderer. At first he is courteous to De Flores, thinking him an honest man (Act 4, scene 1), but later (Act 5, scene 2) takes an instinctive dislike to him and strikes him. At the end of the play he is satisfied that justice has been done.

Vermandero

Vermandero is Beatrice's father. He occupies a high position in Alicant society, since he lives in a castle and is attended by servants and has other employees. He is an old friend of Alsemero's late father, so is well-disposed to Alsemero. He is a good-hearted man, hospitable and honorable who is forced in the final scene of the play to watch in dismay as the evil acts are revealed and his own daughter is killed.