What does it mean to be a good man in this dirty world? How much responsibility do the new-tech billionaires who have transformed society have for an increase in anger and disaffection? Can anything be done to counter and absorb the effects of violence?

These are all good, meaty questions and the subjects of Christopher Shinn's new play Against, given its premiere at the Almeida. But he doesn't find a way of giving them enough momentum to forge a satisfying drama.

His subject is Luke (Ben Whishaw), a Silicon Valley billionaire, who has made his dollars through a series of inventions including moon rockets, solar panels and artificial intelligence. Now, however, he believes he has been called by God "to go where there's violence". The look on the face of his journalistic assistant Sheila (Amanda Hale) when he explains the nature of his revelation is a wonderful mixture of horror and fear that the man she clearly loves has lost his marbles.

But she agrees to help him in his project to heal the world, provided he doesn't mention the God thing. So off Luke goes to the home of the parents of a boy who has committed a school massacre and almost immediately discovers that his initial aim of listening to people and understanding the causes of violence is impossibly complicated by reactions to him. He quickly talks about his conversations with the Almighty and becomes a Christ-like figure, gaining devoted followers who look to him to give them hope, and equal numbers of detractors.

Whishaw and Hale are wonderful, expanding both the story and the relationship. I last saw him filling this stage with whirling energy as the cross-dressing god Dionysus in Bakkhai. Here he is all quiet holiness, still intensity, his agitation revealing itself only in his twitching fingers and restless thumbs. He is a plausible latterday saint but also a hideous prig, full of self-righteousness, leaving Sheila hanging because he can't decide whether he is ready for love. Hale is equally fine in a much less densely written role. Her entire body constantly expresses what she feels, even when she doesn't have a line to say.

But around them, the play rapidly disintegrates into a series of short, pretty evenly paced scenes, which twist and tug into all directions. Some of these are funny – there's a wonderful encounter with a waspish and politically correct creative writing professor (Kevin Harvey) who was a sex worker in a former life – but not all advance the work's central themes. In the second half of a longish evening (nearly three hours), Shinn concentrates on the violence implied and engendered by the exploitation of workers at a world-beating distribution company called Equator (resemblance to another world-bearing distribution company entirely intentional) where Luke plans to make a major announcement.

The contrast between his vision of a peaceful future and the owner's (Harvey again) plan for "relational purchasing", touches on the interesting theme of how commercial assumptions are shaping behaviour more than any ethical or moral concerns. But the points keep getting lost in another short scene that veers in another direction until the entire evening reaches a predictable climax.

What makes it worth sticking with, in Ian Rickson's effortlessly sleek production on Ultz's simple set, are the performances, not just from Whishaw and Hale but from a cast who often play multiple roles with conviction and passion. It's just a pity that we end the evening not so much wiser than we began it; we know what Shinn is Against but not what his play is for.

Against runs at the Almeida until 30 September.