Post Mortem, Pablo Larrain, 98 mins (15)

It's one thing to sleepwalk through a land of atrocities – it's another to wake up in it

Has there ever been a political film as weird – as creepy – as Chilean drama Post Mortem?

Only one that I can think of – Pablo Larrain's previous film Tony Manero, in which the horrors of the Augusto Pinochet dictatorship were presented from the viewpoint of a sociopathic disco dancer morbidly obsessed with John Travolta's character in Saturday Night Fever.

Post Mortem isn't quite as outré on the surface, but it's even more chilling. Its deep strangeness lies in an unearthly tone that makes you wonder whether you're watching a film about living people surrounded by death, or about characters who are – fig- uratively speaking – dead from the start.

Its anti-hero, Mario, resembles a walking cadaver – a pallid, expressionless man, played by Alfredo Castro, who was so impeccably repellent in Tony Manero. Mario works in a morgue transcribing coroner's reports, but could easily be a stiff that's stepped off the slab and helped himself to a lab coat.

The story is set in 1973, and starts just before Chile's military coup. At first there are only hints of the violence to come. The first hour largely deals with Mario's uneasy courtship of his neighbour Nancy (Antonia Zegers), a dancer in a mildewed vaudeville theatre, the Bim Bam Bum, where punters are fed a diet of stale stand-up comedy and creaky cancans.

Nancy, we quickly learn, is as cranky as Mario. Escaping from her house, where her father and a friend hold left-wing political meetings, the couple head to Mario's for a shared weep – in which Mario partakes wholeheartedly, tears and snot streaming down his face in the most off-putting first date scene I've witnessed.

What promises to be a bleak study of a dysfunctional couple takes a shocking turn when the coup happens – but the fatal moment is depicted in an uncanny, economic style that's the opposite of what you'd get if, say, Oliver Stone were in charge. The lightning bolt falls off stage and unseen, while Mario is in the shower. We see his unresponsive head framed in his window, hear thunderous noises (planes, cars, screaming) – then see him step out into the deserted street to find Nancy's house torn to pieces.

It's when Mario returns to work that the film hits its darkest register – partly because of the icy matter-of-factness with which the horror is depicted. The mortuary is under military command, and corpses are coming in by the cartload, piling up in the corridors. All the coroner's team can do is process them, listing types and quantities of wounds, and move on. Thus does the deadly combination of dictatorship and bureaucracy make numbers of everyone.

Post Mortem is neither a reconstruction of the Pinochet days, nor an angry denunciation of the period. Instead, Larrain offers a borderline-surreal – dare I say, Lynchian – black cartoon to show, among other things, how easy it is for ordinary people to sleepwalk into the climate of atrocity, either as victims or collaborators (or, equivocally, like Mario) as both.

Larrain, whose third film this is, has found his "fetish actor" – his own Klaus Kinski – in the skeletal Castro, whose lank locks, drab knitwear and somnambulistic, marionette-like demeanour make his Mario a very pallid, nerdy sort of ghoul. Easily as troubling a presence is Zegers as Nancy, an emaciated flirt as disturbed as Mario himself. Nancy and Mario are made for each other, in a sense: driving through a left-wing demo, eager to get away, they're both delusionally apolitical, clueless about a coming apocalypse that they could never imagine affecting people like them.

Narcotised as the mood is, the film becomes horribly arresting once the slaughter starts. Nothing prepares you for the coolly horrific end shot, a lengthy single act executed like a piece of performance art, that shows how willing Mario is to serve the cause of death, rather than just record it.

The visual style is unsettling – images are topped and tailed, boxed in, so you can't always see what's going on, and cameraman Sergio Armstrong shoots in faded browns, purples and off-greens that suggest a corpse on the turn. The film is intensely shocking, but in a very subtle way: you come out feeling you've been swimming in someone's else nightmare, then remind yourself that the nightmare really happened, and not so long ago.

Next Week:

Jonathan Romney files his confidential report on Tinker Tailor Soldier Spy