The comedy unfolds in fashionable eighteenth century London, where a circle of idle socialites led by Lady Sneerwell thrives on inventing and circulating malicious falsehoods to ruin reputations. Within this environment of social posturing, Sir Peter Teazle finds himself miserable after marrying a young country girl, Lady Teazle, who quickly adopts the expensive habits and frivolous amusements of the town. Lady Teazle is drawn into the orbit of Joseph Surface, a man universally praised as a model of virtue and sentiment, but who is in reality a cold and calculating hypocrite.
Joseph schemes to secure the fortune of Maria, Sir Peter's ward, while simultaneously encouraging Lady Teazle's indiscretions to mask his own ambitions. Meanwhile, Joseph's brother Charles lives as an extravagant libertine, drowning in debt and selling off his family estate and portraits, yet retaining a genuinely generous heart and a capacity for pity that his brother lacks. Their wealthy uncle, Sir Oliver Surface, returns unexpectedly from the East Indies and decides to test the true characters of both nephews by assuming disguises.
Disguised first as a money lender named Premium, Sir Oliver visits Charles and is astonished to find his profligate nephew willing to sell even his ancestral family portraits, yet deeply moved when Charles resolutely refuses to sell the portrait of his uncle Oliver. Later, visiting Joseph disguised as a needy relative named Stanley, Sir Oliver experiences firsthand Joseph's utter lack of charity, despite his endless stream of moral sentiments.
The converging plots reach a crisis during a clandestine meeting at Joseph's library, where Lady Teazle is hidden behind a screen when both Sir Peter and Charles arrive at different times. The screen is knocked down, exposing Lady Teazle and shattering Joseph's virtuous reputation in front of Sir Peter and Sir Oliver. Stripped of his mask, the hypocrite is exposed, while Lady Teazle repents her follies and reconciles with her husband. The play concludes with the exposure of Lady Sneerwell's forged correspondence by a reformed informer, clearing the way for Charles and Maria to unite.
