Going to a rock gig hardly sounds the most taxing of events, but if you suffer from Fragile X Syndrome, it's far more difficult than you can ever imagine.

Tom is one such sufferer. Having Fragile X Syndrome, which is a form of autism, means that he suffers from social anxiety on a day to day basis. As long as he has structure and familiarity in his life, he can get along well enough. But take him out of his surroundings however, and there's a very good chance he will close down and withdraw into himself until he feels safe.

Despite this fragile state, Tom is a huge fan of heavy rock gods Metallica, specifically drummer Lars Ulrich. A mantra he has repeated often over the years is "meet Lars". And it's this request that has spurred his sister Kate, and brother William, to take their brother on a journey of a lifetime.

But with a trip that involves various modes of transport, as well as different time zones, to reach California and follow the band on part of their US tour, taking Tom out of his comfort zone proves to be more challenging than they could ever expect.

Hope to God these two get some work from this, I don't want to make a sequel.

Although on the surface it appears a film about two guilty siblings taking their brother away on a fantastic adventure sounds endearing, it's difficult not to feel a tad cynical about the whole project; after all Kate is a 'lifestyle' journo and although William is described as a filmmaker, this documentary is his first foray into the medium. There's a slightly uncomfortable sensation throughout that the whole concept is more about being a springboard for their careers, and less about their brother's experience.

At one point, whilst Kate is on the phone, one of Metallica's people she's talking to cries out "oh Mission to Lars right?", which kind of indicates that the concept was born out of an admittedly great title at a really early stage, and that there was little room for true spontaneity.

There's also the point that they are travelling a vast distance to see a band on a world tour. By their very definition, a world tour will stop off at old blighty, which begs the question, why put a member of your family through such a traumatic experience if you didn't really need to? A coach trip to the O2 would certainly be less glamorous for all those concerned, that's for sure.

That said, it's difficult not to be touched by Tom's physical and emotional journey. Due to his condition, he struggles to communicate exactly how he's feeling, but his body language says it all. And the film's finale almost wipes away the cynicism created by his sibling's involvement.

The bigger pay off possibly comes however from your willingness to believe the sincerity of Kate and William's intentions, which then lifts this film above your average taking-someone-with-an-illness-to-meet-their-favourite-celebrity fodder.

But even though the film involves members of one of the biggest heavy rock groups in the world, the star of this show is undoubtedly Tom. Even if you ignore the fact that he pretty much gets dragged halfway around the world, somewhat unwillingly, by his brother and sister, there's no denying that it is a trip rich with rewards and one that Tom – and all those who watch him – are likely to ever forget.