The actor-turned-writer/director Matt Ross has been a recognisable indie face for two decades now: he counted among the nightclubbers of 1998's The Last Days of Disco and the cutthroat company men of 2000's American Psycho, and has more recently been spotted amid the ensemble of cult HBO sitcom Silicon Valley. It makes a kind of sense, then, that his latest directorial outing, Captain Fantastic, should in some way be a reflection on living the principled-yet-penniless independent life, a lightly philosophical dramedy - of the type generally lauded at the Sundance Festival - weighing up the pros and cons of going off-grid. These are the misadventures of the ironically named Cash clan, a motherless tribe living in the woods of the Pacific Northwest whose offspring have been schooled by their hippy dad Ben (Viggo Mortensen) in the ways of self-sufficiency and showering under waterfalls. (There's some bagpipe-playing, too.) The call of the wild will be interrupted by a call from the blue. While picking up supplies, Ben learns that his other half, institutionalised with acute depression, has committed suicide, a development that drags him and his well-drilled youngsters back to civilisation on a rescue mission: to reclaim the body from the in-laws in order to give it the Buddhist burial Mrs. Cash had requested.
What follows looks from a distance like one of those culture clashes that has sustained many an American independent venture since the moment of Easy Rider. On one side of the screen, Ross places straggly longhairs who make a point of celebrating "Noam Chomsky Day"; on the other, we see the well-fed squares guzzling on the teat of capitalism. "They look like hippos!," exclaims the clan's youngest Zaja (Shree Crooks) of the well-insulated patrons milling around the bank lobby where these worlds first collide. Yet where we might expect a fight to the death, Ross instead offers broadly affectionate satire, gently ribbing both ends of the political spectrum. Ben's exasperated commentary on what he sees looking out the windscreen of the family's converted bus offers a sustained critique of the American dream, yes; but Ross amuses himself (and us) showing the Cashes' shambling lefty alliance has become plagued by holier-than-thou infighting. "Only a Stalinist would call a Trotskyist a Trotskyite!," objects eldest son Bo (George Mackay), at which point British viewers are bound to find their minds drifting towards the Labour Party's current travails.
Captain Fantastic is an unusual American picture in that it refuses to bear out one side as any more correct or enlightened than the other. True, Team Viggo have conviction, right-on wisdom and its younger constituents aren't glued to a screen, but the normies have pancakes, television and sex, and which sentient humanoid would turn their nose up at any of those? It's telling that one of the first stops the Cashes make upon their return to civilisation is at the all-American household of Ben's sister Harper and her hubby Dave - Kathryn Hahn and Steve Zahn, such an apposite pairing their names even rhyme - whose domesticated happiness and stability don't seem as objectionable as Ben might venture; only an especially militant soul would put these two up against the wall. Ross's script keeps testing everybody's beliefs, and thereby nudges these characters - like a concerned parent - towards a healthy rapprochement, a more lasting and beneficial harmony than might be found out in the woods. Some of this is already latent in the casting. It's become a truism to say that actors-turned-directors are the best directors of actors, but the performances Ross elicits really are very good: the Cashes, to take one key element here, both convince as a ragbag dragging themselves backwards through hedgerows at daddy's behest, and cohere as a family unit with their own history, allegiances and in-jokes.
Crucially, Ross nails the casting of the clan's polar opposites. Frank Langella, an erstwhile screen Nixon, is an especially inspired choice to play the hardline grandfather warding Ben away from his daughter's corpse, and having Mortensen play Ben makes a good deal of sense, too. As written, the character is close enough to Mortensen's established public persona to make Ben's fatherly advice sound sage and sincere, but the star also retains a sense of humour about this dude that works in Ross's favour. He's willing to let everything hang out, but retains the modesty and perspicacity to note that Ben isn't the superhero the (ironic) title would introduce him as, rather a man who - in the absence of a mollifying female presence - has raised his family to serve as his own private army. There are missteps, like the final-reel singalong that miraculously rebrands these cabbage-patch kids as well-rehearsed Glee alumni, and I wonder/worry whether, post-Little Miss Sunshine, a much-trumpeted "Sundance sensation" with this many youngsters in its cast is bound to trigger certain preconceptions: the word "twee" may feature in less forgiving reviews. Sweet-natured and open-minded may be closer to the mark, I'd say: at a point in 2016 where everybody appears more entrenched than ever, solace can be taken from a movie that so obviously sets out in search of the centreground that is our common humanity.
Captain Fantastic screens on BBC2 tomorrow at 10pm, and on Thursday at 12.05am.