Sam Walters' production (which runs until early December with a brief break next month for two triple-bills of G.B. Shaw shorts) is an exemplary illustration of the power of the Orange Tree's intimate in-the-round configuration to breathe vitality into neglected or otherwise arid plays. There is nothing especially revelatory about Walters' take on Shaw's 1905 drama. We see in the first act, as always, how the Undershaft family's haut-bourgeois values are built on estranged father Andrew Undershaft's position as the world's greatest arms manufacturer, selling – as a point of principle as much as commerce – to everyone who can afford to buy. Likewise, in the second, how his daughter Barbara's Salvation Army ideals and spiritual drive are at the mercy of financial exigencies and can be bought and sold by any corporation that finds philanthropy convenient. And in the third, that most Shavian of debates, when the disbursement of the Undershaft arms profits is touted by Andrew as the road to salvation: "Dare we make war on war?"

Octavia Walters' birdlike features are, as ever, a little too expressive: one is always conscious that it is Ms Walters acting, not Major Barbara feeling. Robert Austin as her father does not quite live up to Undershaft's sobriquet "the Prince of Darkness". David Antrobus as Barbara's intended, Adolphus, seems rather too scatty to convince us that this professor of Greek will fulfil either his own ambitions, Undershaft's or Barbara's in running the company. And yet, and yet. In this compact room, with no bank of seating more than three rows deep, on a simple set composed of Undershaft munitions crates so that everything is literally built on armaments, there is far less sense than usual of characters being mere mouthpieces for staged debate: at point-blank range its fire-power is devastating. It makes me wonder whether this is not Shaw's masterpiece, for our age at least. We may now be in a position to appreciate its ethical complexities as we were not even eight years ago when Peter Hall revived it in the West End: we have fewer illusions than ever about corporate, political or even spiritual nobility. When Adolphus and Barbara make their final resolution, we recognise both that it never will work and that it is the only avenue that can. Ethics in armaments? The evening begins with a delightfully vicious Undershaft-flavoured variation on the usual warning about mobile phones.

Written for the Financial Times.