Police corruption of the highest order is on the cards in director Oren Moverman’s follow-up to his much-praised 2009 feature, The Messenger, which once again presents another riveting and eminently watchable turn from his star of that previous film, Woody Harrelson.

The actor is cast here as Dave ‘Date Rape’ Brown, a gleefully un-PC and thoroughly dirty LAPD officer. His questionable policing techniques (the nickname stems from killing a serial date rapist without cause) and blasé attitude towards his superiors and the job itself have gone largely unchecked during his career, but in the wake of the Rampart scandal (a real-life incident back in the late 1990s when a number of cops linked to an anti-gang unit were hauled in due to severe police misconduct) the political implications begin to factor into proceedings and Brown comes under heavy scrutiny in this position.

It’s not just his professional life which is in shambles either. He lives in what is best described as a granny flat behind the homes of his exasperated ex-wives (Anne Heche and Cynthia Nixon) who are actually sisters, and he embarks on an ill-advised affair with a high-flying lawyer (Robin Wright) whose loyalty to him becomes increasingly ambiguous. On top of everything, a recent display of excessive force towards a suspect brings down him into contact with the Deputy DA (Sigourney Weaver) who is looking to make life difficult for him, and a tenacious police investigator determined to bring him to justice (Ice Cube).

Despite all this Brown lumbers on, callous and unrepentant, and seemingly under the impression that his acts are in some way justifiable, but with his life already in freefall, he descends further into the abyss.

Starting off like a grottier version of Training Day (Brown’s guileless, sexist soliloquy towards to a young female rookie really sets up the character early on) Rampart soon transforms into something much more satisfying, and instead presents a measured, complex and involving character study which is more reminiscent of films from that era of downbeat 70’s US cinema (the casting of Ned Beatty as Brown’s crooked mentor is a nod to this) than Antoine Fuqua’s pulpier 2001 crime drama.

While Washington actually picked up the gold statuette for a more overtly showboating portrayal of a corrupt cop, there’s a sad irony here in the fact that Harrelson (utterly memorising as Brown and giving what is without doubt a career-best performance) has been unjustly snubbed by the Academy this year. All the superlatives directed towards his performance are completely warranted and it’s a huge oversight that he’s missing from the awards season, as it’s rare to see this calibre of performance on screen. He completely disappears into the role and no other actor on the planet does gratuitous smoking quite as well either. Even the likes of Don Draper and colleagues would go green around the gills if they attempted to keep up with Brown and his never-ending nicotine intake.

Similar to his previous film, Moverman has a canny grasp of casting quality and seasoned performers to help compliment his star’s turn. Everyone makes a strong impression here – even those who crop up in what are essentially cameo contributions. Ice Cube has seldom been this good on screen, and the actresses who portray the women in Brown’s life are wholly sympathetic despite having been involved with such a loathsome character. ‘Messenger’ co-star (and co-producer here) Ben Foster even crops up as a homeless wheelchair war veteran doing that wiry and intense routine he does so well, but first and foremost, this is Harrelson’s film. When Brown’s world finally reaches stretching point towards the last half of the film, it becomes almost painful to watch the character as he stutter’s through his day, and at one point, pitifully attempts to makes amends with his estranged daughters who pay him a visit at a motel he’s holed up in.

Admittedly, the film is pretty light on plot and the sometimes languid pace and quietly ambiguous ending may not to everyone’s taste, but for those who enjoy adult drama with an emphasis on character and performance (and witnessing a lead actor at the very top of his game), Rampart is essential viewing.