Third Star, Edinburgh Film Festival Closing Gala

Hattie Dalton's Third Star, which was the climax of this year's Edinburgh Film Festival, is pitched between buddy movie and terminal-illness melodrama.

Well enough acted and very inventively shot and directed, it can't help but be dragged down ultimately by its own undertow of mawkishness.

As in William Faulkner's As I Lay Dying (also an inspiration for the book and film of Last Orders), the storyline is about a group of people on a journey that forces them to examine their own attitudes toward love, friendship and mortality. The difference here is that the main character, James (Benedict Cumberbatch), is not a presence from beyond the grave but is still alive.

Suffering from a terminal illness, he has invited his three best friends (all, like him, in their late 20s) to accompany him on a trip to Barafundle Bay, a remote beauty spot on the Welsh coast. He is in no fit state to walk so the three friends transport him on an improvised cart over increasingly rough terrain. En route, tensions between the old friends are exposed. They're forced to confront the direction their lives have taken and the compromises they have all had to make.

Dalton and her director of photography, Carlos Catalan, excel at filming landscape. They capture the austere beauty of a west Wales coastline where the light changes constantly and the weather is unpredictable in the extreme. Dalton is also very effective at conveying the ever-shifting relationships between the four friends who know each others' weaknesses all too well. The further they travel, the less attention they pay to social nicety. James, who knows he is going to die, has no compunctions about telling his friends frankly what he feels their shortcomings to be.

The acting is generally strong. J J Feild offers just the right measure of arrogance and vulnerability in his role as Miles, the alpha-male type who seems to get what he wants very easily (even if he can't fulfill himself as a writer.) Cumberbatch brings a prickliness and a streak of perversity that stops him from seeming like a Tiny Tim Cratchit, however weak and incapacitated he may become. There are some memorable comic set-pieces along the way, among them a full-blooded brawl in a country pub and an improvised firework display that goes badly wrong.

At least initially, the film-makers are aware of the dangers of excessive sentimentality. The dialogue is liberally laced with expletives and sardonic one-liners. At one stage, a character even refers witheringly to the "unnecessary fake soul-searching which everyone is doing these days". Dalton also has an eye for telling but idiosyncratic detail: the mischievous yet angelic-looking kid who taunts one of the travellers; the old ferryman (Karl Johnson) who wears eyeshadow; or the beachcomber (Hugh Bonneville) on a quest for a hoard of missing Star Wars figures he thinks may have been washed ashore.

Despite its painstaking craftsmanship and committed performances, Third Star can't escape its own all-too predictable storyline. Dalton's direction becomes increasingly heavy-handed and we risk entering the bathetic world of TV-movie-of-the-week melodramas.