Jessica Brown's delayed pick for a Carry On Campaign review was actually a list of possibilities, of which I made this choice for selfish reasons: I really love the movie and had never come up with a plausible excuse to review it. Which is turning into a bit of a theme with these. Anyway, it's an excellent subject, and Jessica has my gratitude.

Werner Herzog has a phrase that gets quoted a lot: "the voodoo of location". This refers to the certain aura that a real place can impart on a film shot there, a way that the physical presence of the location affects the cast and crew and even the viewer. It was, in essence, his way of justifying his frequent moviemaking trips into the most godforsaken corners of the Amazon with people who more often then not went insane from the process.

(Okay, so it's not: apparently, the phrase was first use in the context of his Nosferatu, explaining his hope that he could channel the spirit of F.W. Murnau by using the same locations Murnau did in the original).

I bring this up, because the 2001 psychological thriller Session 9 relies on the voodoo of location to an almost inconceivable degree; of course, there have been plenty of horror pictures that get quite a bit of mileage from a gangbuster set, but this is a damn extreme case: I could possibly be convinced that the difference between "Session 9, minor masterpiece of contemporary psycho-horror" and "Session 9, decent, but fatally muddled murder mystery with a bullshit shocker ending" is solely due to that same voodoo of location; and considering that the film's director and co-writer, Brad Anderson, conceived the film specifically to take advantage of a location, I expect he might even agree with me.

The location in question is - was - Danvers State Insane Asylum, located in Danvers, MA from 1874 until the bulk of it was demolished in 2006 (despite being on the National Register of Historic Places) to make way for apartments. Perhaps unwittingly, Anderson and Stephen Gevedon's script prefigures the hospital's ultimate fate, for their film finds the building playing itself, right before some kind of undisclosed construction is about to take place. This construction requires the removal of several rooms full of asbestos and other toxic nastiness, and we arrive on the scene to see Gordon Fleming (Peter Mullan), owner of Hazmat Elimination Company, and his right-hand man Phil (David Caruso) attempting to win the contract from his friend, developer Bill Griggs (Paul Guilfoyle). Their winning bid involves Gordon's frankly desperate and wholly indefensible promise that he can bring the whole project in within one week - with a new baby, Gordon is in dire need of money - and the following Monday, Gordon and Phil start to work with a crew including Phil's romantic rival Hank (Josh Lucas), ex-law student Mike (Gevedon), who is curiously over-fascinated with the institution's history, and Gordon's nephew Jeff (Brendan Sexton III).

It doesn't take long for things to start getting weird; in fact, they were already weird the week prior, when Gordon distinctly heard a disembodied male voice whisper "Hello" as he stared at a chair sitting abandoned, square in the middle of the hallway. He's not the only one being affected by the place: Mike stumbles across a collection of audio recordings of sessions with a patient named Mary Hobbes, suffering from multiple personality disorder: she houses a chatty, flighty girl called Princess and a slightly British boy named Billy, who takes it as his job to protect Princess and Mary from whatever happened Christmas Day, 1951. There's also a third personality, Simon, but nobody is willing to talk about Simon...

First things first: for a genre picture, Session 9 is remarkably concerned with psychology (and why shouldn't it be, taking place in an asylum and all?). The truly striking thing about the film's structure is that fully half of the movie is gone before it starts to resemble a horror movie at all: there's the ghostly voice that Gordon hears, and the unsettling Mary tapes, but the first 55 minutes of the 100 minute film are concerned almost to the exclusion of anything else with the interplay between the five men: Hank is screwing Phil's ex just because he doesn't like Phil, Gordon is freaking out over something that happened between his wife and him, and it's making Phil worried, Jeff needs to have somebody holding his hand every step of the way, and on, and on. It is, grace notes notwithstanding, a chamber drama for most of this time, and nothing less; confining men to a small space for a long time and watching as they fray apart.

After a time, yes, it becomes a horror thriller all the way: someone or something is stalking the men and doing... something. Hank disappears, only to come back two days later mumbling incoherently; and the more Mike listens to the tapes, the more he gets unsettled with what he hears, and obsessed with unlocking their mysteries, going so far as to absentmindedly call Jeff "Princess". Truth be told, it's pretty easy to see where all this is going; you don't need a PhD. in horrorology to guess exactly what's happening to make Gordon fall apart, and really the only open question for most of the movie is whether there's a paranormal angle to all this - if Danvers State Hospital is taken with a malevolent spirit that draws out the latent wickedness in men, a la the Overlook Hotel in The Shining - or if it's simply the strain of what Hank astutely points out is a constantly nerve-wracking job, finally catching up to men who've been doing it too long (they are, let us not forget, professional wranglers of a potent carcinogen). And even this ambiguity exists largely because Anderson decided, in the editing stage, that it would be more mysterious and spooky if he pulled out all the bits where he explained what was going on.

In which belief he was right, so I should probably not be snotty about it. What surprises me, perpetually, about Session 9 is that for a film whose script absolutely does not work in so many ways - the first 20 minutes are home to some particularly excruciating exposition of the "let me talk at great length about something that does not matter because it will strike the audience as foreshadowing" sort, and the result of Anderson's tinkering is frequently not studied ambiguity but borderline incoherence (the debates that have followed the film about exactly what happened, down to the level of whether certain characters exist at all, have less to do with a Lynchian focus on unknowability than with good old-fashioned confused writing); and it's never entirely clear why Mike starts listening to those tapes and thus driving the whole movie along - it's unfailingly successful at doing on thing: it slowly builds up a sense of creeping dread so incrementally that you don't notice that this working class drama of stressed-out men has become a hallucinatory nightmare until the final sequence comes along and you find your skin has wriggled about an inch and a half up your arms.

It's two things what does it. Firstly, the cast is really, really good: Mullan to me is one of the great underappreciated characters actors working right now, and he manages to keep the peculiarly-conceived Gordon perfectly grounded, but there's not a weak link, not even Caruso. It's the easiest thing to believe these men, and the script gives us plenty of time to get to know them before shit goes down; the interaction between them all is natural and unforced, and there's no moment so inexplicable that the actors can't salvage it.

Secondly, is, of course, Danvers State Hospital: a huge building, rotting from within, sweeping and Victorian from without (though some of the exteriors were filmed using a double). As I said, Session 9 without this building is simply inconceivable. Virtually nothing was done to the place to ready it for the cameras; and while the crew was only allowed into a small percentage of the decaying, dangerous institution, they got more than enough. Anderson and cinematographer Uta Briesewitz don't have to do much with outrΓ© lighting - though there is some great use of gloomy blacks later on, when things have already gone haywire - but simply capture the space as accurately as possible; Briesewitz would later shoot a good many episodes of The Wire (a show that Anderson also worked on, briefly), and what's absolutely crazy is that you can see the traces of one in the other: Session 9 has that same kind of realer-than-real urban grittiness that often marked The Wire. Stylised without a doubt, but not the kind of stylisation that gives you the chills. No, Danvers manages to do that all by itself, and here we get to the core of it: the building, in and of itself, is absolutely more inexplicably eerie than any set. For example, the tub of grimy water in the hydrotherapy room was put there by the crew, but not the peculiar tile mural reflected in it; and it's the mural that really seems "off". And that omnipresent feeling of infection, coating the walls and falling from the ceiling and lurkling in the stagnant water here and there: that's real.

In short, the place is just fucking wrong. This, more than anything, carries us over the holes in the script: as written, Session 9 simply asks us to accept that these men start to fall apart for no clear reason, but as shot, Session 9 screams out the reason loud and clear: because they're stuck in a corroded Hell of slimy tile walls and putrid yellow everywhere; it's not hard to believe for one second that simply standing in those rooms would drive the characters 'round the bend, for it would drive me crazy, it would drive you crazy, and frankly, it's a wonder the actors made it through without a hitch.

The questions of whether or not there's a ghost or demon involved; who went crazy and at what point; these are matters to be debated over a post-screening meal, just for fun, but I honestly don't find them terribly interesting. The film's mind-blowing sense of place, now that is interesting; Session 9 is a corker all right, but it's not because of its unresolved questions. It's because of the hulking monster that sits in the center of every frame, a perversity that has the edge of ghosts and hallucinations for the unanswerable fact that it is unambiguously and threateningly real. It is the perfect cinematic embodiment of everything that sounds terrifying about being in an old asylum at night, far more than even the most lovingly detailed set could ever be; and that is the voodoo of location, a depiction of the soul of a place that stretches its chilly hand out from the screen and wraps its fingers around your throat.