She Stoops to Conquer is a comedy of errors that begins with Mr. Hardcastle informing his daughter Kate that Marlow is coming by to visit and that he hopes that the two will marry. Kate is interested, since Marlow is handsome and intelligent, but she has concerns about his alleged timidity around upper-class women. Apparently, this shyness does not extend to working class girls. Kate's cousin Constance confesses her affection for Hastings, Marlow's best friend. Both young men are traveling to the Hardcastle home, but matters do not go according to plan.

Kate's mischievous brother Tony decides to trick the two men into thinking the Hardcastle house is an inn. This causes the men to treat Mr. Hardcastle (who they believe to be a working-class innkeeper) rudely. Constance informs Hastings of the truth, and the two plan to elope once Constance obtains her jewels. Meanwhile, Hastings tells Marlow that Kate and Constance just happen to be at the inn (he does not tell Marlow the truth because he thinks Marlow would only run away in embarrassment). Marlow is uncomfortable around Kate, who is otherwise attracted to him.

The plot thickens when Mrs. Hardcastle, intent on marrying Constance to Tony, learns about her plans to elope and tries to thwart them. Kate later becomes mistaken for a barmaid by the now-bold Marlow, allowing her to observe his natural behavior. Ultimately, Marlow confesses his love for Kate shortly before he learns her true identity, proving himself a worthy suitor. Constance's marriage wishes are saved when Mr. Hardcastle reveals that Tony is actually old enough to refuse Constance as a bride no matter what his mother wants. Being completely uninterested in Constance, Tony does so, leaving her free to marry the man she loves.