In Joseph’s library, Lady Sneerwell is criticizing Joseph for spoiling their plot. She believes that Sir Peter will now support Charles and Maria’s marriage. Joseph is less upset, but Lady Sneerwell says that this is because he does not really love Maria, whereas she truly loves Charles. Lady Sneerwell says that Joseph ruined everything by going too far: he should have stuck to tricking Sir Peter into thinking he was a man of sentiment and stealing his brother’s beloved, but he crossed the line by trying to seduce Lady Teazle as well. Joseph says he is sorry, but he thinks there is still hope. He says that, if Snake can still be trusted, he will help them. Snake has been asked to swear that Charles is engaged to Lady Sneerwell and to produce forged letters as proof.
Lady Sneerwell criticizes Joseph for having taken on too many “projects” and ruining their plan to sabotage Charles and Maria’s engagement. But the two rumormongers have one more trick up their sleeve: they will try to prove that Charles has been carrying on a hidden correspondence with Lady Sneerwell, and has proposed to her. This kind of secret correspondence would, of course, be very unlike Charles, who takes pride in his own openness and honesty, but the rumormongers are so used to dealing with duplicitous people that they think this plot might work.
There is a knock at the door. Joseph says it must be his uncle, Sir Oliver, and tells Lady Sneerwell to wait in the next room. Lady Sneerwell tells him to make sure that his uncle doesn’t discover his true character, and Joseph replies that he is sure Sir Peter will be too embarrassed to tell Sir Oliver what happened and that he will soon discover the best way to manipulate his uncle.
Joseph believes that Sir Peter, like himself, will never admit to anything that makes him look bad and will instead conceal his true emotional state and opinions from others. Sir Peter, however, has learned that concealment can stand in the way of a good marriage and the clearheaded judgment of others.
Sir Oliver enters and, recognizing him as “Mr. Stanley,” Joseph tells him he must leave immediately. “Mr. Stanley” says that he has heard that Sir Oliver will soon arrive, and although Sir Oliver has not been generous with his nephew, Stanley wants to ask for his charity. Mr. Stanley refuses to leave, and Joseph is calling for the servant to drag him from the house when Charles arrives. Charles asks why Joseph is treating his broker “Mr. Premium” so roughly. The two brothers argue over the identity of the man, while trying to forcibly remove him from the house before Sir Oliver arrives.
As the brothers try to get rid of Mr. Stanley/Mr. Premium before their uncle arrives, the wisdom of Sir Oliver’s plan to test his nephews’ true characters before revealing his own identity becomes apparent. He was right that Joseph and Charles would try to keep him from learning anything negative about them. Joseph wants to prevent Sir Oliver from hearing that he told Mr. Stanley he had not received money from his uncle, while Charles hopes to prevent him from learning that he sold the family portraits.
Sir Peter, Lady Teazle, Maria, and Rowley arrive. Sir Peter says he is glad that he arrived in time to save Sir Oliver from being knocked down. Joseph and Charles realize Sir Oliver’s identity and are stunned. Sir Oliver says that he has discovered Joseph’s true character and finds him an ungrateful, ungenerous liar. Sir Peter and Lady Teazle agree. Charles says to himself that he is sure to be judged harshly for selling the family portraits, especially if his brother gets such treatment.
Charles knows that he showed inadequate respect for his family by selling the portraits, and does not know that Sir Oliver has revealed much more serious character flaws in Joseph. Used to having his character judged harshly, especially in comparison to his brother, Charles does not imagine that his uncle will see things any differently.
Sir Oliver then begins to give his impression of Charles, but Joseph interrupts him, saying he wishes to explain himself. Sir Oliver will not listen to Joseph’s attempted explanation, but asks Charles if he too believes he can justify his behavior. Charles tells his uncle that he cannot. Sir Oliver says he cannot be angry at Charles, and laughs at how cheaply Charles sold the heirlooms. Charles says how happy he is to see his uncle, and Sir Oliver says he forgives him his bad behavior.
Everyone can now see through Joseph’s sentimental speeches, and so his attempt to make excuses only makes him look worse. His unwillingness to admit to his bad behavior and apologize is the final strike against his character. Charles, on the other hand, shows that he knows what he did was wrong, which gives his uncle the opportunity to forgive him.
Lady Teazle says that she believes Charles is even more anxious to make up with Maria than with his uncle. Maria does not speak at first, but then says that she is glad to hear Charles is happy—though she knows that he loves someone else. Sir Peter and Charles exclaim in confusion, but Maria says that Charles and Lady Sneerwell know the truth. Joseph then opens the door to allow Lady Sneerwell to enter. She says that Charles has put her in an indelicate situation, and Joseph says that he can produce proof to support what Maria believes: that Charles and Lady Sneerwell are engaged. Sir Peter says he can guess that Joseph hopes to call on Snake, and asks Mr. Rowley to bring in Snake.
Joseph and Lady Sneerwell have convinced Maria that Charles is engaged to Lady Sneerwell, but it is rather farfetched for them to believe that they will be able to force Charles to actually marry Lady Sneerwell just because he promised to do so in a series of forged letters. Joseph, who once thought he could force Lady Teazle to help him marry Maria after he had slept with her, once again overestimates the power of lies to force people to act as he wants them to.
Snake enters and apologizes to Lady Sneerwell: he says that although she paid him well to lie and forge letters, Rowley offered him double her price to tell the truth. As Lady Sneerwell storms from the room, Lady Teazle confronts her, saying she knows that Lady Sneerwell started the false rumor about her affair with Charles, and that she wants nothing more to do with the group of gossipmongers. Joseph says he is shocked and appalled to hear that Lady Sneerwell paid Snake to trick them, but he must follow her and make sure she does not try to take revenge on Charles. Sir Oliver yells after Joseph that he should marry Lady Sneerwell if he can. Snake leaves, asking that they promise not to tell anyone that he told the truth because lying and cheating is how he earns a living.
Even after Snake reveals the last part of Joseph and Lady Sneerwell’s scheme, Joseph still will not admit to his own immorality or wrongdoing. Instead of trying to make excuses to his family, he sees that his last chance to increase his fortune is to marry Lady Sneerwell, so he sets off in pursuit of her. Lady Teazle, meanwhile, is disenchanted with the gossips. Not only have they been cruel to her, but they no longer seem like an impressive clique of sharp-tongued and witty socialites. Instead, they have all made fools of themselves by trying and failing to manipulate others.
Everyone congratulates Maria and Charles on being able to marry now. Sir Peter says he hopes that Maria and Charles will live as happily as he and Lady Teazle intend to. Charles thanks Rowley for supporting him, and Rowley says that he will feel he has been repaid if Charles mends his ways. Charles says that he will not promise anything, but that this is also proof that he will sincerely try to be a better man. The play ends with a verse recited by Charles. He says that he will be inspired to better himself by marrying Maria.
Charles has shown that when it counts he is motivated by feelings of loyalty, generosity, and love. He affirms that Rowley was right to see through his bad behavior and understand that he is actually a principled man. Married to Maria and as Sir Oliver’s heir, his wealth will increase enormously, but he pledges to be worthy of this investment in his future.