The 1988 comedy-drama Rain Man won Oscars for its writer (Barry Morrow), director (Barry Levison) and star (Dustin Hoffman), as well as the Academy’s principal award for Best Picture. It’s clearly reckoned a pretty fine piece of work, then. When we can all so easily watch it on DVD, one wonders at the reason – beyond the turning of a fast buck – for translating this justly famous film into a play for the stage.

The decision is more surprising in the light of the fact that Rain Man is a road movie, a celebration of the American landscape as well as a detailed study of the relationship between the two brothers we follow on their six-day journey through it.

Any feel for the great outdoors is utterly eliminated from Dan Gordon’s adaptation. The action remains obstinately within walls. At first these belong to the institution in Cincinatti to which the autistic savant Raymond Babbitt is confined, until his wheeler-dealer younger brother Charlie – who was previously unaware of his existence – ‘springs’ him. Charlie’s aim is to use him as a pawn in securing a share of their late father’s substantial will from which he has been unfairly excluded.

Next we shift to an airport, from which Raymond, with his encyclopaedic knowledge of airline accident statistics, steadfastly refuses to fly on their journey west. Instead they go by car (we never see it) towards Los Angeles, with nightly motel stopovers, and a detour to Las Vegas where Raymond is able to assist Charlie in winning a shedload of cash at blackjack through his astonishing ability to count cards.

The concentration on the brothers’ relationship at the expense of almost everything else makes huge demands on the skills of the actors playing them. Neil Morrissey (pictured right, above) gives a moving and credible portrait – necessarily reminiscent, of course, of Hoffman’s – of the damaged, childlike Raymond, with his devotion to routine and order, his fear of change, of emotional involvement.

Oliver Chris (left), as Charlie, convincingly shows how the character’s brittle and abrasive personality is slowly transformed under the benign influence of his brother. True, there is a thick streak of sentimentality here, as there was in the film – and certainly where Charlie’s impossibly perfect, utterly understanding girlfriend Susan (Ruth Everett) is concerned. But who minds a bit of sentimentality in a good cause?

Until Saturday. Box office Tel: 0844 871 7652 (www.ambassadortickets.com/miltonkeynes).