I.i Alsemero is leaving on business when he meets Beatrice-Joanna in the port town of Alicant. All ideas of business fly from him, and, against the better advice of his friend, Jasperino, Alsemero decides to stay and woo Beatrice-Joanna. This he does until he learns of her imminent marriage. He determines to continue his business abroad. When Beatrice-Joanna returns Alsemero's love, however, he changes his mind again, decides to stay, and determines to challenge Alonzo to a duel to decide who will marry Beatrice-Joanna. Beatrice-Joanna does not like the idea of risking her beloved Alsemero in a duel and seeks another way of ridding herself of the once-loved Alonzo.

A knobby-faced courtier named DeFlores, whose very sight makes her hate him, fondly loves Beatrice-Joanna. But she determines to use DeFlores in her plans to keep Alsemero safe. She persuades him to kill Alonzo secretly. She promises to pay him well for his services. He swears to do her bidding and will ask for his payment afterward.

I.ii Meanwhile, two servants of Vermandero, Antonio (Tony) and Franciscus, have entered Alibius's insane asylum as inmates (neither knowing of the other's plans). They each plan on wooing the old doctor's young wife, Isabella, and cuckolding old Alibius. In the asylum, acting as caretaker, is another old fellow named Lollio; he also has designs on Isabella. Fearing Isabella's unfaithfulness, Alibius keeps her guarded within the asylum whenever he is out.

II.i Upon the arrival of Alonzo and his brother, Tomazo, into Alantia, Tomazo suspects at once that Beatrice-Joanna is none-too-happy to see her intended husband. He is, of course, correct, but Alonzo is too much in love to recognize her indifference.

II.ii Beatrice-Joanna meets Alsemero secretly. Diaphanta leads him to her mistress' room where the lovers exchange love talk. DeFlores spies upon them. DeFlores makes several misogynistic asides, suggesting that virgins become insatiable once they are deflowered. He meets Beatrice-Joanna after the lovers part and again assures her of his fidelity to their plan.

S.D. A stage direction at the beginning of act three informs us that during the act-time (e.g. intermission) Deflores enters and hides "a naked rapier" on stage.

III.i To pass the time before the wedding, Alonzo requests that DeFlores direct him on a tour of the castle. DeFlores seizes the opportunity to lead Alonzo into a thin corridor where one cannot pass with one's weapons on. He entreats the unsuspecting Alonzo to leave his weapons on a peg then leads him through the narrow corridor.

III.ii They reenter immediately into another room in which DeFlores has concealed a sword. There, while he distracts Alonzo's attention with the scenery from the window, DeFlores retrieves the hidden sword and stabs Alonzo to death. He finds a diamond ring on the dead man's finger, but when it will not come off DeFlores cuts off the finger to have the ring.

III.iii Meanwhile, at the asylum, Alibius is away and Lollio tries to entertain Isabella by displaying the latest fool and madman to her. They turn out to be Tony and Franciscus. They behave like fools and madmen while Lollio is watching but seek to court Isabella when Lollio's back is turned. Isabella does not know what to make of them at first, but soon begins to favor Tony. After the fools' entertainment, Lollio locks them back in their rooms. He makes a pass at Isabella. She rebuffs him. Alibius comes home with the news that he has been requested to present an entertainment at the wedding of Beatrice-Joanna and Alonzo, using the madmen as entertainers.

III.iv Vermandero approves of Alsemero, so much so that he wishes that he could marry him to Beatrice-Joanna's sister, a double of Beatrice-Joanna (perhaps a twin). The girl is dead, however, and Vermandero is given new reason to regret her death. This, of course, is all part of Beatrice-Joanna's plot to ingratiate Alsemero into her father's affection so she might marry him when Alonzo is discovered missing.

DeFlores comes to tell Beatrice-Joanna that Alonzo is dead. He shows her the ring he took from Alonzo. Beatrice-Joanna tells him that it was the first token her father made her send to Alonzo. She tells DeFlores to keep it in earnest for his services and promises to pay three thousand gold florins for his work. When he balks at the reward she offers to double it, but DeFlores insists that only carnal knowledge of her will pay for his services. She has no choice but to submit. DeFlores threatens to betray the whole plot, even at the peril of his own life, if she does not yield to him.

Act IV: In a dumb show, we see the nuptials of Beatrice-Joanna and Alsemero. DeFlores' self-satisfaction indicates that his price has been paid before the wedding night. Deflores is in turn haunted by the specter of Alonzo.

IV.i Beatrice-Joanna is fearful that her new husband will discover that she is no virgin to his bed. She pretends to her serving maid, Diaphanta, that she is fearful of losing her maidenhead-deathly afraid in fact-and she convinces Diaphanta to go to bed with her husband in her place and later to tell her what the experience is like. She offers gold, a thousand ducats, for this service. Diaphanta, not unwilling to bed with the handsome Alsemero, agrees.

Beatrice-Joanna has happened across Alsemero's laboratory-where her new husband dabbles in physics-and discovered a liquid that can tell whether a woman is a virgin. It is a milky liquid in a bottle marked "M." If a woman is a virgin, the potion will first make her gape, then sneeze, next laugh, and finally grow melancholy. In order to satisfy herself that Diaphanta is a virgin-and thereby assure the success of her plan-she asks Diaphanta to drink some of the potion, not telling her what it is, but drinking some herself in order to demonstrate that it is not harmful. It has, of course, no effect on Beatrice-Joanna, but it causes Diaphanta to gape, sneeze, laugh, and grow melancholy.

Beatrice-Joanna's plan is set. She contrives with Diaphanta that Diaphanta should go to Alsemero's bed, have sex with him so that he will think it is Beatrice-Joanna's maidenhead he is taking, and then contrive to slip out of bed around midnight. Beatrice-Joanna will then sneak in beside Alsemero and be discovered there in the morning, thus completing the illusion.

IV.ii Alonzo's absence grows more troublesome. Alonzo's brother, Tomazo, suspects foul play. Vermandero demands to know who of his servants has been gone the ten days since Alonzo's disappearance. He is told that Antonio (Tony) and Franciscus have been gone all that time.

DeFlores avoids Tomazo, seeing his guilty act reflected in his victim's brother's eyes.

Tomazo suspects Alsemero of the deed under an unspoken theory of cui bono. That is, because it was Alsemero who benefited from Alonzo's disappearance then he must be responsible for it.

Jasperino tells Alsemero that he heard Beatrice-Joanna and DeFlores in the next room. They were apparently making love. Alsemero refuses to believe it, knowing that Beatrice-Joanna hates the sight of DeFlores. But Jasperino assures him that he and Diaphanta heard the deed committed. This news surprises Alsemero for two reasons:

1) he knows, or thinks he knows, that Beatrice-Joanna hates DeFlores, and
2) Beatrice-Joanna has just sent Diaphanta to tell him that she is so shy about the wedding night that she wants to come to him in total darkness.

IV.iii In the asylum, Lollio now knows of the duplicity of Tony and Franciscus. He helps Isabella by lending her clothes so that she may pretend to be a madwoman. Tony's great argument to her has been that she should love him despite his fool's clothes. She should see his innate nobility beneath. But when he fails to recognize her under her madwoman's disguise, she rejects him.

Lollio convinces the unmasked Tony that Isabella really loves him, but another suitor like himself, Franciscus, bothers her. Lollio convinces Tony that he must rid her of this Franciscus after the masque. Lollio then turns to Franciscus and tells him much the same story about Tony.

V.i Meanwhile, at the castle, the clock has struck one and Diaphanta has not come out to allow Beatrice-Joanna to take her place in bed beside Alsemero. Beatrice-Joanna fears that Diaphanta is enjoying Alsemero too much and will ruin the plan. She decides that Diaphanta must die. At two o'clock DeFlores meets Beatrice-Joanna, who is still waiting on Diaphanta. He fears that the exposure of Beatrice-Joanna will also expose him. He contrives to set Diaphanta's empty bedroom on fire. He will lie in wait for the guilt-ridden Diaphanta, who will rise and flee towards her chamber (for fear of being discovered not to be there). When she approaches he will shoot her.

The plan is so good that Beatrice-Joanna begins to love DeFlores. He now represents salvation to her, and she finds him desirable. But Alonzo's ghost still haunts DeFlores; though he considers the ghost a mere fancy of his, Beatrice-Joanna is also aware of it as it passes them in the corridor.

At the striking of three o'clock DeFlores raises the cry. Diaphanta, as expected, enters, running to her chamber. Just as she gets out of sight, Vermandero and Jasperino enter to see what the commotion is about. DeFlores enters with his loaded "piece" (gun). He explains that he suspects Diaphanta's chimney has stopped up and caught fire, and that he intends to clear it with a gunshot up the flue. For this Vermandero and Jasperino consider him a quick-thinking and noble fellow.

The gun discharges offstage, and DeFlores returns with the news that the fire has consumed Diaphanta while she slept. The plan has worked.

V.ii Next day, Tomazo is out of his head with grief over the disappearance of Alonzo. He begins to suspect everyone and has a fancy that the next person he meets will be the murderer. The next person happens to be DeFlores, the murderer indeed. Tomazo picks a quarrel, but DeFlores, fearing the reminder of his victim in the victim's brother's eyes, backs away from the challenge and makes excuse that he understands the mental turmoil of Tomazo. He therefore refuses to take offense.

Alibius and Isabella have come to Vermandero and told him that his two gentlemen, Tony and Franciscus, are at the asylum incognito. The circumstantial evidence points to their guilt in the disappearance of Alonzo. They had asked leave to go to Briamata. To be found in a nearby asylum incognito is most suspicious. Vermandero turns them over to the wrath of Tomazo, mainly to appease his guest and to clear up the matter.

V.iii Jasperino reports to Alsemero that he has seen Beatrice-Joanna and DeFlores in yet another trysting place. Alsemero again confronts Beatrice-Joanna. Beatrice-Joanna, caught, tells him that he is guilty of making her a bloody villain. She relates how she got DeFlores to murder Alonzo so that she and Alsemero could be together. The news does not work the desired effect of making him love her the more. In fact, it has quite the opposite effect. He orders that she be locked up in his room.

Alsemero next confronts DeFlores with his newfound knowledge of DeFlores' sin. When DeFlores learns that Beatrice-Joanna has confessed his part in the murder of Alonzo, he tells Alsemero about her whorishness and asks to be allowed to see her. Alsemero sends DeFlores to his room where Beatrice-Joanna is locked.

Vermando brings Tony and Franciscus on to tell Alsemero that the guilty have been caught and will stand the punishment Tomazo chooses. Alsemero reveals what he has learned of Beatrice-Joanna and DeFlores. Tony and Franciscus are set free. DeFlores, after stabbing Beatrice-Joanna offstage (her cries are nearly orgasmic), carries Beatrice-Joanna in to them. He makes her confess about the bed trick with Diaphanta and how Diaphanta met her end. He confesses to Alonzo's murder. DeFlores then produces a penknife and stabs himself. Beatrice-Joanna dies asking Alsemero to forgive her. Tomazo is satisfied that the guilty are punished and seeks no more revenge in Vermandero's castle.

The play ends with Alsemero, Antonio, Franciscus, & Alibius saying how they have changed-and with Isabella saying how she will yet change Alibius (into a cuckold). The image of changelings is thereby made patent.

This is the madcap Tony character that ultimately lent his name to all madmen, who were nicknamed "Tonies" during the eighteenth century.