After Wishfort leaves the room, Mrs. Fainall enters to warn Foible that Marwood saw her with Mirabell in the park and will tell Wishfort. Foible plays it coy because she does not know whether Mrs. Fainall is in on Mirabell’s secret plan to marry Millamant. Mrs. Fainall reveals that she knows about Mirabell’s entire plan, including Foible’s marriage to Waitwell that very morning.
Another case of dramatic irony, as all of Foible’s precautions to figure out Mrs. Fainall’s allegiances are ultimately useless because Marwood is hidden in the closet. As Mrs. Fainall reveals everything she knows about Mirabell’s plan to prove her trustworthiness, that plot is in fact falling apart because Marwood is learning all about it.
Foible explains that she wasn’t sure whether Mirabell told Mrs. Fainall the entirety of his plan to marry Millamant. She compliments Mirabell for being such a good gentleman and Mrs. Fainall for being so generous, and adds that Mrs. Fainall still “has his heart.” Foible also updates Mrs. Fainall on Wishfort’s eagerness to get married.
Foible apologizes for doubting Mrs. Fainall and regains her favor by remarking on how important Mrs. Fainall is to Mirabell and alluding to her former relationship with Mirabell. As Foible updates Mrs. Fainall on the progress of Mirabell’s plan, she solidifies their sense of solidarity.
Before leaving the room, Foible asks Mrs. Fainall to give Mirabell an update about Wishfort’s interest in Rowland and that Marwood seems to be watching them. Mrs. Fainall exits with Foible, taking the servant’s staircase to avoid running into Marwood.
Foible’s fear that Marwood is watching them is an instance of dramatic irony because Marwood is literally watching them right now, though only the audience realizes it.