Wherever I may roam: "Mission to Lars"

Up until now, the public profile of Metallica drummer Lars Ulrich has been that of the huffy grump who stopped Napster in its tracks, and of the huffy grump observed storming out of recording and group therapy sessions in 2004's documentary Some Kind of Monster. This difficult rep hasn't deterred Tom, the reluctant protagonist of the genuinely lovely British documentary Mission to Lars, from wanting to meet his idol. Tom has Fragile X Syndrome, which sounds like a band name waiting to happen, but turns out to be an extreme form of autism; his sister Kate, a London-based journalist, and his cameraman brother Will, have determined to help Tom realise his dream, partly as a way of getting him to stop going on about Lars, and partly as a way of getting closer to the sibling their family shuttled off to a care home in the country. This other Will-and-Kate are recognisable London media types: prone to stress and heavy drinking, and just the teensiest bit self-absorbed, as borne out when Kate oversleeps on the eve of the party's departure for L.A., causing Tom to go on the lam for a bit. He, it transpires, needs the comfort of routine more than the thrill of the road, and a triple-A pass dangling from a lanyard may, for him, prove no compensation for the rigours of jet lag, having to tour a cold, wintry California in the back of an RV, or being pushed towards a moshpit full of seasoned, sweaty metalheads.

In the age of Derek and the Daldrified Extremely Loud and Incredibly Close, projects that dodged giving their protagonists' conditions a name, lest they offended or alienated anybody in doing so, it's encouraging to see something so specific - so honest - on the joys and challenges of co-habiting with the differently abled. Metallica may be the ultimate goal here, but the siblings take a worthwhile detour to the offices of an expert in Fragile X, and a meeting where Tom finds himself deputised as sound recordist, in effect giving him the responsibility of communicating the essentials of his own mental and physical state to the world. It's a film of ostensibly modest means, perhaps fated for a TV slot if More4 could only tear themselves away from Jamie and Grand Designs repeats, but it offers ample illustration of how the American landscape can yield big, romantic images to even a three-person crew, and a reminder of just how important support networks are in lives such as these: everyone the film introduces us to - from the care-home heroes to the earringed ex-tour manager, from Tom's stepmother to the bassist in Slayer - is fully committed to giving Tom the chance to expand his horizons. The final scenes have a real feelgood charge, venturing as they do the thesis that, even within the labyrinthine corridors of corporate stadium rock, there is still a place for ordinary people caught in an extraordinary moment. And - though this may be a spoiler of sorts - Lars himself comes out of it pretty damn well indeed. Enter sandman, exit huffy grump.

Mission to Lars is touring selected cinemas nationwide; an itinerary can be found here.