Gus Van Sant's 'suicide rehab' film is blighted by ridiculous contrivances and overwrought performances

Matthew McConaughey’s last two roles had him exiting the planet (in Interstellar) and finding the right drugs to stay put, in the Aids drama that won him an Oscar, Dallas Buyers Club. In Gus Van Sant’s The Sea of Trees, he’s chosen another path, packing a bottle of painkillers with which he intends to overdose and end things. The film takes its title from a notorious destination at the base of Mount Fuji: Aokigahara, a place also known as the “suicide forest”. Some 100 dead bodies are discovered there every year, and it’s a setting that can't help but feel like a haunted no-man’s-land between life and death.

McConaughey’s character, an American maths professor called Arthur Brennan, begins the film boarding a flight to Tokyo, and the film tips the wink repeatedly – far too repeatedly – about the purpose of his trip. He leaves his car keys dangling from the ignition, the parking ticket on the passenger seat. An airline employee, possibly put up to this by screenwriter Chris (Buried) Sparling, quizzes the poor guy pointedly about booking his return flight – he doesn’t want one, OK! – and asks why he has so little luggage. All the while, a plinky-plonky score of deadly incongruity, by the symphonic composer Mason Bates, nudges him through check-in and security. You round this prologue more anxious about the film than you are for its main character.

Van Sant re-established himself in Cannes as a director worth taking seriously when he won the Palme d’Or for Elephant back in 2003. His output since then has had its highs (2008’s Milk) and lows (2011’s Restless, universally panned for its kamikaze ghost character and cancer plot).

The Sea of Trees, alas, never looks as though it’s headed anywhere but the latter direction. In the context of an already invigorating Cannes competition line-up, it’s likely to suffer a bleak fate indeed – if no other film emerges as the festival’s designated critical punch-bag, Van Sant may claim this dubious honour practically by default.

Arthur wanders deep into the forest to meet his destiny, passing human remains here and there, and encountering a disturbed stranger, Takumi (Ken Watanabe), who's wracked with second thoughts and wants to find the path back out. “Some are certain, some change their minds,” is the explanation Takumi gives us, along with “You do not understand my culture”, a line that should have given the screenwriter pause. While Arthur holds steadfast to his original resolve, trying to help the other man back to civilisation only strands the two of them in a barren purgatory of slip-and-slide outdoorsy strife.

Meanwhile, there are flashbacks, explaining Arthur’s extremity of despair with a blow-by-blow account of his marriage problems, after an affair that changed everything. His wife Joan is a bitter alcoholic who develops a brain tumour: come the end, this is the least of her problems.

Perhaps the greatest warning signal is that she’s played by Naomi Watts, a terrific actress at her best, but one whose regular association with trauma and misery, in films such as 21 Grams, We Don’t Live Here Anymore and The Impossible, makes it hard to give a fresh account of the most sheerly unlucky character she’s ever played. Joan is a kind of greatest hits Watts performance, a Who’s Afraid of Naomi Watts?, and while she and McConaughey go at it committedly, their scenes have the unbelievable, very acted rhythm of canned domestics closing early on Broadway.

The twist Sparling inflicts on her – it’s his first of two megaton contrivances – is a head-slapping insult to credibility, a real boo-from-the-back-of-the-house shocker. And it’s not the worst part, because even when you think the film’s over, it’s plunging back into the forest for a ridiculous final rug-pulling that might have tempted even M Night Shyamalan to go back to the drawing board.

Van Sant wanted to study a man drowning in sorrow and guide him towards the light. But the guidance he gets is fake, forced, and unbearably tricksy, a kind of suicide rehab with gotcha devices. Like Aokigahara itself, the whole film needs cordoning off with safety rope and ""Keep Out" signs. There's nothing to see inside.