The story concerns an idealistic young woman, Barbara Undershaft, who is engaged in helping the poor as a Major in the Salvation Army in London.

An officer of The Salvation Army, Major Barbara Undershaft, becomes disillusioned when her Christian denomination accepts money from an armaments manufacturer (her father) and a whisky distiller.

He points out that donations can always be used for good whatever their provenance, and he quotes a Salvation Army officer, "they would take money from the devil himself and be only too glad to get it out of his hands and into God's."

During their reunion, Undershaft learns that Barbara is a major in The Salvation Army who works at their shelter in West Ham, east London.

A subplot involves the down-and-out and fractious visitors to the shelter, including a layabout painter and con artist (Snobby Price), a poor housewife feigning to be a fallen woman (Rummy Mitchens), an older laborer fired for his age (Peter Shirley), and a pugnacious bully (Bill Walker) who threatens the inhabitants and staff over his runaway partner, striking a frightened care worker (Jenny Hill).

When he visits the shelter, Mr. Undershaft is impressed with Barbara's handling of these various troublesome people who seek social services from the Salvation Army: she treats them with patience, firmness, and sincerity.

Barker also played Cusins, alongside Louis Calvert, Clare Greet, Edmund Gwenn, Oswald Yorke and Annie Russell.

A film adaptation of 1941 was produced by Gabriel Pascal, and starred Wendy Hiller as Barbara, Rex Harrison as Cusins and Robert Morley as Undershaft.

A TV movie production was broadcast in 1966 with Eileen Atkins as Barbara, Douglas Wilmer as Undershaft and Daniel Massey as Cusins.

[2][4] Andrew Undershaft was loosely inspired by a number of figures, including the arms dealer Basil Zaharoff, and German armaments family Krupp.

Undershaft's unscrupulous sale of weapons to any and all bidders, as well as his government influence and more pertinently his company's method of succession (to a foundling rather than a son), tie him especially to Krupp steel.

Wiesenthal has discussed parallels with the play and Shaw's personal interpretations of Richard Wagner's Der Ring des Nibelungen.

[14] Norma Nutter has briefly discussed conflicts between the character's personal convictions compared to the social realities that they eventually face, via the concept of 'false consciousness'.