The other denizens of the shelter return from a public fundraiser. Barbara recounts how Price moved a crowd with his confession. When Jenny tallies the contributions, Undershaft offers to add two pence. Barbara refuses his money because he has blood on his hands and cannot buy his salvation. She asks Cusins to write her another donation letter for the newspaper. The winter has brought starvation, everyone is unemployed, and the shelter will close without more funding. Barbara laments having to think more of collection than people's souls. "Genuine unselfishness is capable to anything my dear," remarks Undershaft ironically. "Mephistopheles! Machiavelli!" exclaims Cusins in an aside.

Suddenly Bill reappears with frost on his jacket. It comes from the ground in Canningtown. Todger knocked him down and knelt on his head to pray for him with Mog. Barbara enjoys the story frankly and Jenny expresses her sympathy. Bill refuses Jenny's Christian forgiveness and offers to pay her to square their debt. Barbara forbids Jenny from even taking his money for the Army. Undershaft offers to add ninety-nine pounds to Bill's one if Barbara accepts. Barbara is unmoved. Bill sullenly leaves his sovereign on the drum, stealthily Price drops his cap on it.

Mrs. Baines, an Army Commissioner, then enters. Barbara introduces her father. When Undershaft notes civilly that the nation knows of the Army's work, Baines laments their shortage of funds. Recalling the riots of 1866, she calls Price forth to confirm how the Army keeps him from revolution. Price skulks off, taking Bill's sovereign with him.

Baines announces a miracle, and says that the Lord Saxmundham has promised the Army five thousand pounds if five other gentleman will give one thousand each to make it ten. Undershaft reveals to his daughter that the lord is the former Sir Horace Bodger, the distiller, who received a baronet upon restoring the Hakington cathedral. To Baines' joy, Undershaft promises to help them meet Saxmundham's condition. "Wot prawce selvytion nah?" scoffs Bill in an aside to Barbara.

Barbara interjects and wonders whether they have forgotten the evil of Bodger's distilleries. Baines reminds her that Bodger has a soul to be saved too. Undershaft ironically remarks that alcohol makes life more bearable. He also claims his own disinterestedness, remorselessly conjuring the horrors of war to note that every convert the Army makes is a vote against war and a step toward his commercial ruin. Overtaken in an "ecstasy of mischief," Cusins cheers Bodger and Undershaft; Barbara almost crumbles when her fiancé fails her.

The group makes ready for a triumphant procession through the streets, Cusins playing the drum to the chorus of "For thee immense rejoicing—immenso giubilo—." As he notes, "Dionysus Undershaft has descended," and he is possessed. Barbara refuses to join them, pinning her silver S brooch on her father's collar. "Blood and Fire" cheers Baines as the group exits. Jenny cries "Glory Hallelujah" and Undershaft yells "My ducats and my daughter" yells Undershaft. Cusins screams "Money and gunpowder," and Barbara closes with "Drunkenness and Murder! My God: why hast thou forsaken me."