Summary
Beatrice-Joanna is anxious that Diaphanta is enjoying her sexual encounter with Alsemero too much. DeFlores promises to start a fire in the castle and cause commotion that will separate them. Beatrice-Joanna tells DeFlores that she is now forced to love him because of his service to her. This time, they both see Alonzo's ghost as they part.
Once the fire starts, chaos breaks out. Diaphanta returns to Beatrice-Joanna, who is curt with her and sends her back to her bedchamber (where DeFlores had started the fire). Meanwhile, DeFlores walks around with a handgun, saying he plans to clear out the chimney. The gun goes off later, and DeFlores appears, telling everyone that Diaphanta has died in the fire.
Tomazo continues to search for his brother's killer, even accusing DeFlores but ultimately withdrawing his accusation. Vermandero tells Tomazo that he suspects the killer was two nobles who have been hiding in a madhouse, but Alibius informs him that Antonio and Franciscus have since left town. Tomazo vows to find them.
Back in Alsemero's chamber, Jasperino convinces Alsemero that something is going on between Beatrice-Joanna and DeFlores. Beatrice-Joanna arrives, and Alsemero pressures her to explain. While she initially feigns ignorance, she eventually confesses to her conspiracy with DeFlores and the murder of Alonzo. Alsemero locks Beatrice-Joanna in his cupboard, and eventually locks DeFlores in with her.
Alibius comes to the castle with Antonio, Fransiscus, and Tomazo. While they are sorting out Alonzo's murder, they hear a loud noise from the cupboard and open it to find DeFlores and a wounded Beatrice-Joanna. Vermandero realizes that his daughter was part of the murder plot, and Beatrice-Joanna confesses to Alsemero that it was Diaphanta who slept with him on their wedding night, not her.
Fearing punishment, DeFlores kills himself, saying "Joanna" with his dying breath. Beatrice-Joanna follows suit. Alsemero forms a new bond with Tomazo, and they comfort Vermandero, who is lamenting both the death of his daughter, the betrayal of his servant, and the conspiracy between them.
Isabella asks Alibius to loosen control over her and to fire Lollio for someone more trustworthy. Alibius vows to change into a better husband.
In the Epilogue, Alsemero mourns the casualties of the play while encouraging honesty and continued community.
Analysis
The events of the play build to the action of Act Five, where all that has been concealed until this point is ultimately revealed.
In the final step in the transformation of the relationship between Beatrice-Joanna and DeFlores, Beatrice-Joanna expresses genuine care and attraction toward DeFlores for the first time when he agrees to start a fire in the castle. It is his service Beatrice-Joanna emphasizes, rather than his physical appearance, that draws her to him, as she finally sees him as strong and masculine as he agrees to aid her in her deception. This encouragement from Beatrice-Joanna only increases DeFlores passionate love for her, but to a new point of villainy: DeFlores shoots Diaphanta in cold blood, fearing that Beatrice-Joanna is jealous of her after she slept with Alsemero.
DeFlores's behavior represents another one of the play's major themes – the effects of passion on one's moral compass. DeFlores and other characters blindly follow their passions rather than tempering those passions with logic, and it is ultimately this pursuit of passion that leads to his (and Beatrice-Joanna's) demise. The play therefore warns against this type of blind pursuit, which was so often idealized on the Renaissance stage. In many ways, DeFlores and Beatrice-Joanna represent a perverted version of star-crossed lovers who act out of their own agency and create their own tragic fate.
Notably, the play ends with a tragic central plot and a comic subplot (nobody from the madhouse plot dies), once again using the two plots as foils for one another. Isabella vocalizes this relationship between the two plots when she tells Alibius that he has been too controlling and too stern with her; she notes the chaos of the castle as the "real" madhouse, and suggests that he be more trustworthy of her because she would never behave like Beatrice-Joanna.
Though this plot may seem completely irrelevant to the tragedy of the main plot, it ultimately showcases in miniature many of the character flaws that the central plot featured on a large scale, notably the men's desire to control women and their bodies. When Alibius vows to be a better husband, he is effectively atoning for the failures of those men – DeFlores, Alsemero, and himself – who prized virginity and possession above all else.
