The conveyor belt of Hollywood stars in film adaptations rolls on as Josh Heartthrob comes to town. Despite some misleading publicity material, he is playing Charlie Babbitt, the part created on celluloid by Tom Cruise in Barry Levinson's popular movie, and not his colourful brother, Raymond the Rain Man.
It is left to English actor Adam Godley to recreate a role for which Dustin Hoffman won an Oscar in 1988 and is still so fondly remembered.
Hartnett is not a natural stage actor and, early on, gives the impression that he knows it. Gradually, he thaws into at least a passable performance as the two-hour long play gets going after the interval.
The opening scenes, played out in narrowed down, unexciting, film-inspired spaces, portray a caveman whose business is on an unstoppable slide. Why his pretty girl, given charm by Mary Stockley, hasn't ditched the disreputable conman must remain a mystery.
It is no surprise that having failed to mourn his father's passing, Charlie is incandescent to discover that "his" inheritance is going to a trust for a mysterious beneficiary.
To this point, every reaction has been wooden and it is only the advent of Godley that rescues his director, Terry Johnson, who might be considered a specialist in this kind of American film transfer to the London stage, having already directed The Graduate and One Flew Over the Cuckoo's Nest.
The British actor might not be Dustin Hoffman but he gives a heart-warming performance as the autistic savant, part little child, part genius. He is the focal point of an evening that overdoes the sentimentality but does give us a few good laughs and, maybe for the very soft-hearted, a tear or two but not many more.
Gradually as he is kidnapped into a picaresque journey of discovery, some sparks of humanity and normality are injected into his elder brother by Charlie. Much against character, the shameless fraud begins to find his own soul too, learning as much about the give and take of life by the end as Raymond has.
The audiences will flock to see Josh Hartnett's muscular frame and rugged good looks but will come away more impressed by Godley's acting than that of their film hero.
Fans of the movie are unlikely to compare this stage version favourably with the original, which might not bode well for a long run, although Mr Hartnett's commitments might not permit that anyway.
Visit our sponsor 1st 4 London Theatre to book tickets for Rain Man.