Act III opens in Newgate, following Macheath's undramatized escape through the use of Lucy's key.
Standing by the empty hold, Lockit confronts Lucy, who tries to blame Polly and Peachum. Lockit refuses to believe her, instead wondering whether he might make more off of Macheath's bribe to Lucy that he would have from his split with Peachum. However, Lucy quashes this dream by confessing that she helped Macheath for free.
Lockit then reminds her how she was raised in alehouses, where he taught her to keep careful record of who drank what so they could cheat the patrons. He wonders how such an upbringing could have ruined her sense of money, while she suggests that the alehouse upbringing is what ruined her. She then sings an air which suggests that the alehouse introduced her to the danger of men’s kisses.
While speaking with Lockit, Lucy realizes that Macheath has probably run straight to Polly, and chastises herself for her foolishness, worrying Polly will steal his money and turn him over to Peachum. She sings an air exploring the violent offense Polly has done her, after which Lockit banishes Lucy from his sight.
Alone on stage, Lockit schemes to outwit Peachum, and reflects on the way man "preys upon his neighbor" and yet will "herd together" with those neighbors nevertheless (p. 53). He then sings an air about dice-playing friends who help one another cheat dupes at their table. When there are no dupes present, they cheat each other.
Lockit receives word that Filch is drinking with Black Moll next door, and summons him. Filch arrives, looking rumpled and spent from the gang's women, who have been having sex with him in hopes of growing pregnant and therefore protecting themselves from hanging.
From Filch, Lockit learns that Peachum is currently at the warehouse where he stores his stolen goods (called a 'lock'), located at the Crooked Billet. Lockit readies to go there.
The action of Scene IV shifts, to a gaming-house.
There, Macheath — now dressed in a roguishly fine coat — bursts in to find his friends Ben Budge and Matt of the Mint. Knowing his friends are in need, Macheath distributes some money recently 'won' on the highway. He sings an air about court friendship, asserting that courtiers sell each other out for a profit, while his gang displays superior honor.
Together, the friends plan their evening, intending to surveil gamblers and then afterwards rob them on the highway.
The action shifts, to Peachum's lock (or warehouse for stolen goods).
There, Peachum and Lockit sit at a table loaded with wine, brandy, and tobacco, discussing the accounting complexities for goods stolen from the crowd gathered at George II’s Coronation. Because the items might be recognizable, they can only be sold to trustworthy vendors. Peachum finally decides the matter is too complicated for the moment, and Lockit agrees.
Lockit then warns Peachum to keep a watchful eye on Polly, as Macheath will soon be returning to town. He sings an air about the deceitfulness of women, particularly their daughters.
A servant announces the arrival of a Mrs. Diana Trapes, who then enters, stinking of drink. Both men taste the gin on her lips as she kisses them in greeting. Mrs. Trapes sings an air contrasting young lips, which belong to other lips, and old lips, which belong to liquor.
Mrs. Trapes has come to collect clothing for resale, even though she has been unable to pay the men what she owes for their previous exchanges. She confesses that times have been tough since the Act for Destroying the Mint was passed. (The Mint was an area of sanctuary for insolvent debtors and wanted criminals.) Before the Act was passed, she always knew where to find someone who owed money. Now, these debtors are imprisoned and cannot be coerced to pay by a criminal. She tells how one of her employees - Mrs. Coaxer - had just that night returned after having fled a debt. Catching Mrs. Coaxer, Mrs. Trapes forced her to sexually service Captain Macheath in order to earn some money towards what she owed.
Realizing that Mrs. Trapes has access to Macheath, Peachum offers both to sell her the clothes cheaply and to pay Mrs. Coaxer's debt if she will allow them to take the man. Mrs. Trapes agrees, taking an extra scarf in the bargain.
Back at Newgate, Lucy is alone. She sings an air that expresses anger at Polly and despair over Macheath. Then, she announces her plan: she has summoned Polly to the prison, and will poison the girl with rats-bane. Filch enters to announce Polly’s arrival.
Once Polly enters, Lucy apologizes for her previous behavior, and sings an air attesting to the frightful, capricious moods of women. Polly, in turn, apologizes for her own behavior. Lucy suggests they drink a glass of cordial together, to celebrate their friendship. Polly declines, claiming that cordial induces headaches. They both apologize yet again, blaming their passion for Macheath as the cause of their previous animosity. They then sing a duet together, the gist of which is that men flee from overfond women.
After the song, they acknowledge that each indeed has grounds to be jealous of the other. Polly sings a short air likening men to coquettes. Lucy then again prevails on Polly to drink a glass with her, and sings an air to make the offer sweeter. Of course, she means to kill the girl.
Polly delivers a soliloquy, revealing that she perceives the malice in Lucy’s offer, but cannot discern the exact plan. Instead, she believes Lucy intends to intoxicate her in an attempt to wring Macheath’s secrets from her. She resolves not to drink.
Lucy threatens to take offense if Polly will not drink, but the latter holds fast. They are interrupted when Macheath is suddenly brought in, prisoner once again. Polly crumbles at the sight of her beloved in chains, and Lucy feels relieved that her plan was not completed, since Polly "was not happy enough to deserve to be poison’d" (p. 65).
The women rush to Macheath, whom Peachum and Lockit have bound. Together, they sing an air entreating him to choose one of them, but he responds that he need not choose since he is soon to die.
However, Peachum insists Macheath choose in order to prevent any lawsuits between the women after his death. In response, Macheath sings an air about the impossibility of his choice: "One wife is too much for most husbands to hear / But two at a time there’s no mortal can bear" (p. 66).
On her knees, Polly begs Peachum to suppress the criminal evidence against Macheath, singing an air that attests to her grief and heartbreak. Lucy then kneels to beg mercy from her father, and sings an air preaching pity. But Lockit is immovable; he sings an air insisting that Macheath’s time to die has most naturally arrived.
Peachum is equally unyielding, and he and Lockit prepare to bring Macheath to the Old Bailey. Macheath sings an air asserting that he is ready to die, if only to settle this unbearable dispute. The men then leave.
Polly then sends Filch to follow their fathers, and to report back every detail of Macheath’s demise.
Once alone, the women notice music coming from an adjacent room; it is being made by the prisoners whose trials have been postponed until the next court session. Polly is momentarily enlivened by the music, but quickly enough lapses back into sorrow. Heartbroken, the women leave together.
Meanwhile, the dancing prisoners — all in chains — come tumbling in.
The action shifts to the cell meant for condemned men.
There, Macheath drinks heavily and sings several airs in quick succession, a medley of tunes. The gist of this medley is that his sole remaining friend is alcohol. Nevertheless, he admits he will miss women. He then envisions swinging from the branch of a tree.
Ben Budge and Matt of the Mint arrive to bid Macheath a fond farewell. His last request is that his friends endeavor to see Peachum and Lockit hanged before they themselves hang. The explicit suggestion is that everyone will eventually hang. Ben and Matt swear to honor Macheath's requests, and then exit.
Lucy and Polly enter, weeping and pathetic. Macheath advises them to seek new husbands in the West Indies, where English women are in high demand from criminals sent to the colonies.
Macheath, Lucy and Polly sing in trio. The women sing of their despair, how they wished they would be hanged, too. Macheath laments the failure of his liquid courage; he has run out of drink. And then they hear and sing the toll of the bell, the death knell: "Tol de rol lol" (p. 71).
A jailor announces the arrival of four more women to see Macheath. These women enter, each lady trailing a child behind her. Macheath panics to see "four wives more," and sends word that death is preferable to this situation (p. 71).
Macheath is led away to be hanged.
The Player and The Beggar reappear to discuss the play’s ending. The Player cannot believe that the Beggar truly intends Macheath to hang. However, the Beggar most certainly does: "To make the piece perfect, I was for doing strict poetical justice" (p. 71).
The Player argues, however, that this ending marks a tragedy, whereas operas must end happily. The Beggar concedes the point, and directs the rabble to “...cry a reprieve—let the prisoner be brought back to his wives in triumph” (p. 72).
Macheath, the rabble and the women return to the stage. Macheath proposes they perform a dance through which he will select his one, true wife. He pairs up the women and the men, selecting Polly Peachum as his partner...for life. After all, they are already married.
Everyone dances as Macheath sings an air which concedes that every man must eventually choose one woman. The ensemble takes up the chorus of the song: "But think of this maxim, and put off your sorrow / The wretch of to-day, may be happy to-morrow" (p. 73).
The final act of the play both reflects the play's main themes and reveals Gay's masterful ability as a storyteller. As he effectively presents two endings - one arguably moral, one decidedly amoral - he forces his audience to confront his ideas as he simultaneously fulfills its expectations for opera.
Most centrally, the idea that every person seeks his or her self-interest remains paramount. Scenes VIII, IX and X center on Lucy’s attempt to poison Polly through a false show of remorse and reconciliation. Even though it would gain Lucy little to murder Polly, she will gladly do it for the sake of revenge. Meanwhile, Polly shows her maturity when she immediately suspects Lucy of a ruse. It is interesting, though, that Polly never voices her suspicions, no matter how shrill or insistent Lucy becomes. Instead, both women attend to the other with a veneer of civility, throwing asides at the audience to reveal their true thoughts.
This formula — ladies fighting through a veneer of civility — fell very much in line with the world of Restoration Comedy and its portrayal of female rivals. William Congreve’s Way of the World serves as the prime example of this style. Gay’s play nods at his predecessor’s comedy of manners but eschews any inclusion of the aristocracy. This whole scene is a wonderful example of how Gay's irony works. He presents an opera conforming to the expectations of high-class behavior, while consistently undercutting that behavior to show the depravity of which every man is capable.
The poisoning scene also hearkens back to the Introduction, in which The Beggar promised to include all the necessities of a well-made opera. One such operatic reference is the use of poison, an oft-employed melodramatic flourish from the imported Italian operas of the day. The threat of poisoning in this Newgate context, however, is positively ludicrous. After all, these women are not tragic, romantic heroines; they are simpering, misguided, conceited, gullible girls, bleating about their love for an absolute cad. The use of poison is another ironic send-up of an operatic trope.
The send-up of opera goes even deeper, as the feud between Lucy and Polly is in fact a thinly veiled satire of the gossip-column feud between two of the day’s leading sopranos, Francesca Cuzzoni and Faustina Bordoni. The Introduction would have reminded a contemporary audience of this feud, when The Beggar assures the audience that he has distributed the actresses’ roles evenly, so as not to offend either woman.
Bordoni, it seems, was paid a higher salary than the more established Cuzzoni. Bordoni was also praised as having a better voice and for being more beautiful. But Cuzzoni had her own fan base, and their respective supporters and detractors grew vicious towards one another. In 1727, one year prior to the debut of John Gay’s play, a brawl broke out upon the London stage during the performance of an opera in which both ladies starred. The newspapers thrilled to its reportage, accusing the women of hair pulling, eye scratching and the most unladylike of name-calling. By alluding to this feud, Gay is not simply referencing a contemporary event, but is in fact going deeper into his mockery of the elitist form.
All in all, friendship is painted quite poorly in this act. When Polly actually falls into sorrow upon seeing Macheath brought into Newgate, Lucy feels less angry about failing to poison her. The suggestion is that friendship is inherent treacherous. There is no true amity where a friend’s good fortune exceeds one’s own. There is real philosophical weight in such observations, but Gay’s masterful burlesque always keeps the tone light.
The one notable exception to this theme is the friendship between Macheath and his friends Matt of the Mint and Ben Budge. Macheath lends them money seemingly from genuine concern, and they never betray one another. It would be tempting to suggest Gay means to claim there is more honor amongst thieves than amongst statesmen, but he has provided too many instances of thieves willfully betraying one another for such an interpretation to stick. Regardless, it is an interesting exception.
The end of the play follows a scene in which the Player and Beggar dispute the Beggar’s intended ending, wherein Macheath would hang for his crimes. When the Player insists that the Beggar lighten the tone, he is mocking the improbably reconciled endings of the era's operas. The Beggar agrees with this reasoning - and so, of course, do we. We might leave the play thinking about his ideas, but we also leave entertained by the very conventions Gay simultaneously skewers. John Gay has created a world so absurdly robust in its critique of the highborn, the lowborn and everyone in between, so incisive in its equating of statesmen and courtiers with petty thieves and prostitutes, that the audience may no more condemn Macheath to swing from Tyburn tree than condemn themselves to the self-same branch.