Cusins then makes a shocking confession. When he met Barbara, she bought his soul for God but herself—or rather, "Dionysus and all the others" in herself. Only later did he realize that she was an aristocrat and thus had to lie about his birth. His parents' marriage is legal but in Australia, his mother being his father's deceased wife's sister. Britomart snorts in contempt.
Even though Cusins is still an educated man, Undershaft accepts him nonetheless. He will change his name and begin with a salary of a thousand pounds a year. Cusins demands five thousand and ten percent of the profits after his third year. His soul should be capital enough, and Undershaft agrees to three-fifths.
Sorrowfully Barbara asks if Cusins's soul now belongs to Undershaft. Undershaft insists that Cusins cannot simply sell arms. He must subscribe to the true faith of the Armorer: to give arms to all men who offer him an honest price, nationality, faith, and cause notwithstanding. He lists the mottos of the Undershafts before him, ending on his own: Unashamed. Cusins refuses and has more power than Undershaft, as Undershaft ultimately belongs to the foundry.
The latter part of Act III consists of the family visit to the Undershaft's ideal community. The family marvels at the success of his social engineering and they note the careful enumeration of all Perivale St. Andrew's amenities. Even Britomart is enchanted with the "civilized living" materialized in the houses, gardens, and furniture. We should observe that Perivale is imagined entirely from the perspective of the aristocrat family. Bilton, the only worker and town resident on the scene, appears as a sort of "straight man" for comic relief. Certainly the pleasure this visit lends the family and the audience partially lies in being on the inside of the experiment. For example, Lady Britomart can disapprove of the church motto as being cynical, whereas its congregation might not. Note also in this respect the patronizing, affectionate reference to Peter's embarrassment before the gate lodge.
In this section, Undershaft appears as social engineer par excellence. A certain rhetoric of "common sense"—a rhetoric typical among proponents of social engineering, whether at home or abroad in the empire—becomes especially apparent in his speech. For example, in responding to Stephen's concern that the social services of the community might make the workers lazy, Undershaft explains that "when you are organizing civilization you have to make up your mind whether trouble and anxiety are good things or not." Under the banner of common sense, Undershaft's plans appear logical, self-evident, obviously the right thing to do to create the greatest good. Suggestions to the contrary—such as those implied in questioning Undershaft's self-appointed change to "organize civilization"—are not admissible.
These scenes also continue the elaboration of Undershaft's gospel, which promises salvation to man by freeing him from a poverty that renders him inhuman or criminal. Undershaft's ideal community is not built by these working men, but through the mystical "will" of which Undershaft is a part. This "will" is the Undershaft tradition, the will of the arms industry which Cusins, as successor, must assume "unashamed." As Barbara will come to realize, it is the Undershaft will, rather than God's, which redeems the world.