George Bernard Shaw's play, Major Barbara, delves into the complexities of morality, wealth, and social responsibility. Opening in the London home of Lady Britomart, the narrative explores her concerns about securing financial futures for her children. With tensions between family values and the stark realities of industrial capitalism, the play unfolds over three acts.

Act I

The play begins in Lady Britomart's library, where she discusses her worries with her son Stephen about their family’s financial prospects. Her daughters, Sarah and Barbara, are engaged to men who cannot yet provide for them—Charles Lomax awaits an inheritance, and Adolphus Cusins, a scholar with limited income, is romantically involved with Barbara, a fervent Salvation Army officer. Lady Britomart’s resolution is to consult her estranged husband, Andrew Undershaft, a wealthy munitions manufacturer, for financial support, despite their long separation.

Stephen learns that he will not inherit his father's arms business, as tradition dictates the heir must be a foundling. Shocked by his father's profession, Stephen is further disturbed to discover that Undershaft is expected to visit the family soon. The rest of the family, including Barbara and her fiancé Cusins, join the conversation with Lady Britomart.

Barbara is excited to meet her father, hoping to "save his soul," while Undershaft arrives showing interest in the Salvation Army's "Blood and Fire" motto. Despite discomfort from the family regarding his war-related business, Undershaft remains unapologetic. A mutual agreement is made: he will visit Barbara’s shelter, and she will, in turn, visit his factories, each aiming to "convert" the other.

Act II

The next day at the Salvation Army shelter, the scene is set with Snobby Price and Rummy Michens, who feign sins to gain the Army's charity. Bill Walker causes a disturbance, accusing Jenny Hill of taking his girlfriend and violently confronting those present. Barbara's response is calm and compassionate, which slowly instills remorse in Walker.

Undershaft arrives, observing Barbara’s interactions. He converses with Cusins, revealing his belief that wealth and power are essential for true salvation. Cusins, admitting his love-driven adoption of Salvationist values, finds common ground with Undershaft in their shared affection for Barbara.

Undershaft proposes a substantial donation to the Army, which Barbara rejects, deeming his money unethical. Walker returns, offering money as penance, but Barbara seeks only the salvation of his soul. The Army’s commissioner, Mrs. Baines, arrives with an offer of a significant donation, conditional on matching funds from others. Undershaft agrees, sparking a crisis of conscience in Barbara, who refuses to participate, seeing the Army's reliance on morally questionable funds as hypocritical.

Act III

Returning to Lady Britomart’s library, Barbara appears without her Salvation Army uniform, signaling her disillusionment. Discussions over breakfast reveal Cusins’ night spent discussing ethics with Undershaft. As they prepare to tour Undershaft's model town and factory, Lady Britomart discusses financial arrangements for her daughters with her estranged husband.

Despite Lady Britomart's appeals, Undershaft insists on passing his business to a foundling, not Stephen. Cusins emerges as a potential heir, citing his questionable legitimacy under English law, aligning with Undershaft's tradition. As Cusins negotiates his future with Undershaft, Barbara reflects on her shattered ideals and resolves to find new purpose.

The scene shifts to Undershaft's impressive industrial establishment, where the beauty and order of Perivale St. Andrews astound the visitors. Lady Britomart suggests Cusins inherit the business, but Undershaft adheres to his tradition. Cusins, revealing his willingness to lead the enterprise, negotiates his terms while Barbara critiques the ethical implications.

Barbara, recognizing the material comforts provided to the workers, contrasts them with the deprivation she witnessed at the shelter. Undershaft challenges her to forge a new path, free from poverty’s grip. Alone with Cusins, Barbara accepts his decision to join her father, realizing her mission lies in transforming the community from within.

As the entourage exits the factory tour, Barbara asserts her commitment to saving the town’s inhabitants from spiritual and moral stagnation. She enlists her mother's help in selecting a home among her father’s properties, marking the beginning of a new chapter in her life and mission.