What, yet another movie transposed to the stage, as if to say that there aren’t enough original plays to keep our actors happy? But, though Dan Gordon’s adaptation doesn’t add anything to Barry Levinson’s film, there’s one good reason for seeing it. That’s not the Hollywood star Josh Hartnett, though in many ways he’s as strong as Tom Cruise on the screen. It’s the British actor Adam Godley, who more than matches Dustin Hoffman’s Oscar-winning performance in 1988.

At root this is simply a feelgood variation on two well-worn genres, road and buddy movies. Hartnett’s Charlie, a cool, fly car salesman on the brink of bankruptcy, discovers that his estranged father has willed his millions to Godley’s Raymond, the autistic sibling he never knew he had. So he abducts his brother from the Cincinnati sanitorium where he has been closeted for aeons and, since the young man refuses to fly with him to LA, drives him there via Las Vegas.

Since Raymond is a savant, with a lightning memory for everything including cards, the casinos stand no chance. In an episode that is too cursory and, anyway, occurs offstage, the men make a killing before reappearing for a psychiatric assessment in LA. I won’t reveal what happens when the once-cynical Charlie finds himself protecting Raymond from the shrinks, except that the ending is less clear but also less sentimental than in the film.

Hartnett’s problem isn’t that he lacks the casual egoism his role demands or overdoes the warmth he begins to feel for Raymond. It’s that his admirable energy has an unfortunate side-effect.

It’s as if he were fuelled by high-octane petrol, revving up his vocal cords so that, especially at first, words flash by like clusters of racing cars dangerously tailgating each other. Terry Johnson, who directs, should help him to slow down and unjam this verbal grand prix.

But he should do nothing to change Godley. With his spindly, bent body, his gawky shuffle, his wizened, frowning face, his fits of hand-fluttering panic and long moments of utter stillness, Godley’s Raymond looks far more the victim of long-term damage than Hoffman. He sounds that way, too, half-bleating his refrain of “don’t know”. You never doubt that he is as cut off as a hermit on an iceberg. It is sometimes funny, often touching and always distressing.

The original script has been updated, so that Raymond cites 9/11 as the reason he won’t fly United and can tell you the day and time when Oprah Winfrey will be deciding whether anorexia is “an eating disorder or a lifetime choice”. But that’s incidental. What matters is that you leave the Apollo feeling the pain and poignancy of an affliction as intransigent in 2008 as it was in 1988.

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