There is an idea of Louis Bloom; some kind of abstraction. But there is no real Louis Bloom – only an entity, something illusory. And though he can hide his cold gaze… he is simply not there.

I’m sure American Psycho’s Patrick Bateman wouldn’t mind being paraphrased to describe someone whom he would no doubt approve of.

Louis is a go-getter in the truest sense of the word; a guy chasing his share of the American Dream who also happens to be a sociopath and a monster made flesh by our insatiable appetite for blood-soaked true crime.

Screenwriter Dan Gilroy’s directorial debut turns over the bright and shiny rock of TV news to reveal the desperate putrescence beneath. It may not be particularly earth-shattering to lay bare the grisly cynicism that constitutes the US media machine – Sidney Lumet’s peerless Network did that almost 40 years ago – but Nightcrawler succeeds by wallowing in the muck with the leeches who feed the ‘if if bleeds, it leads’ TV news culture, in particular new kid of the block Lou (Jake Gyllenhaal).

When we first encounter Lou, he’s being caught stealing metal fencing by a security guard, whom he beats up. Even at this early juncture, it’s plainly obvious that something isn’t right with the guy and our unease is heightened further when he attempts to fence the fencing to a scrap yard owner and angles for a job at the same time; all the while quoting self-help book rhetoric and fixing the person in front of him with a rictus grin his saucer eyes fail to match.

It’s an affectation we discover he puts on for everyone and when he stumbles across Joe Loder’s (Bill Paxton) freelance film crew shooting footage of a car crash in order to sell it to the Los Angeles news networks, the missing link falls into place for Lou, who buys a camera and dives headlong into the venal world of ‘nightcrawling’.

With the assistance of intern Rick (Riz Ahmed), a down-and-out looking for a break, who goes along for the ride for a measly few dollars despite knowing his employer is a few slices short of a loaf, he hurtles around the city and sells on his grisly footage to vampire shift news director Nina (Rene Russo) with a self-assured expectation rarely seen since The King Of Comedy’s Rupert Pupkin that he will become a major TV news player.

Bravely, Gilroy eschews backstory for his unhinged protagonist and hands it over to the audience to mull over how Lou arrives where he does. He comes across as almost as blank a slate as Scarlett Johansson’s extraterrestrial visitor from Under The Skin and certainly has the same singular drive, while his mesmeric bug-eyed stare (made more striking by Gyllenhaal’s weight loss for the part) brings to mind the description of many a little green man.

It’s great to see Russo back on the big screen in a part deserving of her talents and it’s fascinating watching her character reduce from alpha dominance (her description of TV news as “a screaming woman running down the street with her throat cut” being a case in point) to Lou’s lap dog as she relies more heavily on his macabre footage and falls under his spell.

Likewise, Ahmed in his breakout US role following a series of very strong roles in such British fare as Chris Morris’ Four Lions, is the only emphathetic character on screen (save for Kevin Rahm’s aghast news editor) and becomes trapped by Lou, who cruelly dangles the prospect of a pay raise based on a non-existent “performance review”.

Needless to say, though, this is Gyllenhaal’s movie and he really goes for it, giving a career best turn in the process. Gyllenhaal has generally been at his best when playing misfits or obsessive types in such films as Donnie Darko (2001), Zodiac (2007) and last year’s Prisoners and amps it up here to a previously untapped level. Lou is a truly unrepentant figure and is as mesmerising as he is appalling.

Less successful is James Newton Howard’s fist-pumping score, which is presumably meant as the soundtrack that Lou has swirling around his head as he goes about his nightly activities (akin to Taxi Driver); however, it doesn’t really come off and ends up becoming distracting. A gripe, albeit a small one.

A remarkably assured debut from Gilroy featuring a tour de force performance by Gyllenhaal, the wickedly disturbing Nightcrawler will crawl under your skin and stay there.