Summary
DeFlores takes Alonzo on a tour of the castle, hiding a rapier in his clothing. He asks Alonzo to remove his own weapons and Alonzo complies.
In front of a vault in the castle, DeFlores stabs Alonzo several times. As Alonzo dies, DeFlores attempts to pry a diamond ring from his finger, but it will not budge. DeFlores cuts off the finger with the intention of bringing it to Beatrice-Joanna.
Meanwhile, in the madhouse, Isabella is locked in her quarters. She asks Lollio to meet the new madmen who have arrived. Lollio brings in a fool named Franciscus, who starts a fight with Lollio and is sent away.
While Isabella is meeting Antonio, Lollio leaves to handle a fight that has broken out. Antonio confesses to Isabella that he is not actually mad, but only pretending because he is passionately in love with her. Isabella rejects his advances.
After Antonio is sent away, Lollio, too, thrusts himself on Isabella, but his efforts are interrupted when Alibius returns with news that the madmen will perform at the upcoming wedding at the castle.
At the castle, DeFlores reveals the severed finger to Beatrice-Joanna, who is appalled. She tells him to keep the ring as part of his payment, but DeFlores is horrified that she thinks he only killed Alonzo for money.
DeFlores informs Beatrice-Joanna that they are now linked forever, and the only payment he will accept is her losing her virginity to him. Beatrice-Joanna protests extensively, but eventually relents.
Analysis
Act Three of the play returns audiences to the subplot involving Isabella, Alibius, Lollio, and the alleged "madmen."
In this part of the play, audiences learn that the "madman" Antonio is not actually mad but is instead a nobleman in Vermandero's castle who is feigning madness is order to get closer to Isabella. While the plot itself is whimsical and a drastic departure from the central plot in which Alonzo is murdered by DeFlores, this comic plot ultimately introduces the theme of appearances and reality to the play. Antonio's disguise as a madman is what gains him access to Isabella. Likewise, Lollio dons a type of disguise as well, portraying himself as a loyal assistant to Alibius when in reality he, too, is attempting to seduce Alibius's wife. All these disguises, both physical and behavioral, serve to comment on the severity of the central plot, which also features characters pretending to be something they are not.
Indeed, this disguising and deception is precisely the meaning behind the play's unique title. A "changeling" is a term from English folklore. It denotes a child believed to have been left in place of a family's real infant, which was stolen by fairies. Over the years, "changeling" came to connote an imposter or substitution, which is operative in this play both in the madhouse and, as audiences will see, in the plot involving Beatrice-Joanna and Diaphanta.
While Beatrice-Joanna does not wear a physical disguise in the play, one could argue that she disguises her own wickedness in order to appear innocent and charming to Alsemero. In what is likely the play's most famous speech, DeFlores confronts this false advertisement Beatrice-Joanna has put forth, calling her a "whore" and arguing that by conspiring with him, she is just as guilty and just as wicked as he is. DeFlores uses language related to twinning, fate, and doubleness to emphasize their indelible connection and ultimately convince Beatrice-Joanna that she has no choice but to make this a physical connection as well. The argument is not unlike the famously flirtatious poem "The Flea," by John Donne, in which the speaker argues that since the blood of him and his lover were already mingled when a flea bit them both, they might as well mingle once again by having sex. Of course, DeFlores is threatening rather than flirtatious, and essentially blackmails Beatrice-Joanna into sleeping with him.
This moment represents a crucial turn in their relationship, which moves from repulsion to transaction to affection over the course of the play.
