The Faith Machine, Royal Court Theatre, London

"The real world is cruel and harsh and full of compromise," is the defensive declaration of Tom, a young New Yorker who was once an aspiring novelist and has now sold out to advertising. For Sophie, his English girlfriend, that amounts to buck-passing. The world is not a given, or an alibi; it's what you make it. So on the morning of 9/11, she confronts her lover with an ultimatum: she will dump him unless he drops the account he has landed with a pharmaceutical company that is illicitly testing its products on Ugandan children.

Alexi Kaye Campbell is astute about the tricky erosion of ideals –witness his play The Pride, which examines the differing pressures on gay men in the 1950s and now. But The Faith Machine, his sprawling, preachy new piece – now premiered in a well-acted but strangely uncompelling production by Jamie Lloyd – feels at once deficient in ambiguity and divided in purpose. Jumping around in time between 1998 and 2011 and in place between New York, England and the Greek island of Patmos, it's a set of variations on the theme that man cannot live by bread alone.

There's a very good moment in the second scene when Sophie's father, an Anglican Bishop (played with a fierce flamboyance by Ian McDiarmid), is countered by the Kenyan cleric who has been sent to persuade him not to resign from the Church because of its intolerant stance on homosexuality. If it followed the bishop's views, he argues, the Church would quickly die in Africa, leaving Islam to reign supreme. And then what would happen to gays? But that is one of few instances of genuine dialectical tension in a play where the author's mouthpieces are allowed to spout unnaturally eloquent soundbites insufficiently opposed.

The dice prove to be loaded, too, in the treatment of Sophie (an impressively "earthed" Hayley Atwell). Heroic reporter from the world's trouble spots or a hectoring prig who has denied her instincts in favour of a life of vicarious suffering? Tom (all frenetic, rootless fluster in Kyle Soller's striking performance) is driven to think the latter. But instead of leaving you fruitfully in two minds as had seemed to be its aim, the play wheels on a heart-tugging new character in a unearned final scene that shamelessly simplifies this maddening, contradictory figure as an undercover saint.

To 1 October (020 7565 5000)