Act III opens in Lord Goring's library with an impeccably dressed Goring and his impassive servant Phipps, named in the stage notes as the ideal butler. A short exchange ensues, in which Goring, trying on a new buttonhole, delivers a series of epigrams regarding fashion, vulgarity, falsehood, and self-love to the yes-saying Phipps. Phipps then brings Goring his letters, and the Lord discovers that Lady Chiltern has sent him a note on pink paper imploring him for help: "I want you. I trust you. I am coming to you." Though it is signed Gertrude, it is addressed to no one.
Though it is late, Goring prepares for her arrival. Phipps, however, abruptly announces the arrival of his father, Lord Caversham. Goring receives him and the two discuss the prospect of Goring's marriage and his adopting a serious career, Caversham posing Sir Robert as an ideal model. Sending Caversham to the smoking room, Goring quickly tells Phipps that he expects a female visitor and instructs him to show her into the drawing room.
Suddenly a bell rings, and Goring moves to answer but is intercepted by Caversham and must accompany him to the smoking room. Mrs. Cheveley then appears on the scene; Phipps informs her of Goring's instructions and shows her into the drawing room. Pleased at the prospect of catching him out, Cheveley rifles through his papers and discovers Lady Chiltern's letter. Just as she moves to steal it, Phipps enters and shows her into the drawing room. Upon his departure, she re-emerges and creeps toward the writing table anew, but must retire upon hearing the voices of Goring and Caversham.
After a brief exchange on marriage and common sense, Goring leads Caversham to the door, only to return, somewhat haplessly, with the unexpected Sir Robert. Sir Robert reports that Lady Chiltern knows all; moreover, the Vienna embassy has failed to excavate any secret scandal from Mrs. Cheveley's past. Goring keeps Lady Chiltern's request for assistance secret.
Phipps then enters, and Goring, taking him aside for further instruction, learns that the lady he expects waits in the drawing room. He decides to give the would-be Lady Chiltern a lecture through the door, prompting Sir Robert to declare his love for his wife and suggesting that she has already forgiven him. Just as Sir Robert is about to reveal what he plans to tell the House regarding the canal scheme, he hears a chair fall in the next room. Though Goring hopelessly tells his friend no one is in the next room—this deferral of the inevitable raising the scene's tension—Sir Robert bursts through and of course discovers Mrs. Cheveley. He curses the unsuspecting Goring for his treachery and storms out; Mrs. Cheveley emerges, beaming with bemusement.
One can divide this part of Act III according to its two major exchanges: one between Lord Goring and his butler Phipps and another with between Goring and his father, Lord Caversham. Both comment on the dandy lifestyle.