Based on a story from "LA Confidential" novelist James Ellroy - veteran purveyor of dark yarns about the City of Angels' demonic flipside - and scripted by "Training Day" writer David Ayer, "Dark Blue" depicts the early 90s LAPD as a breeding ground for brutality and racism. It feels frighteningly authentic.

Tellingly, Ellroy originally planned to set this amorality tale against the backdrop of the 1965 Watts Riots. Instead, the action plays out in the days leading up to the 1992 LA Riots, which followed the acquittal of the police officers who beat black motorist Rodney King. The era has changed. The attitudes haven't.

A prime example of an old school law-enforcer is Detective Sheldon Perry (Kurt Russell). Partnered with rookie rozzer Bobby Keough (Scott Speedman), he's sent by squad chief Jack Van Meter (Brendan Gleeson) to collar two trigger-happy perps who went kill-crazy in a convenience store. Van Meter's not bothered about getting the right guys. In fact, he'd rather they didn't...

With its zinging, streetsmart dialogue and compelling central character, "Dark Blue" never bores. It does, however, frustrate. The attempt to blend fact and fiction flounders - the King references sometimes feel forced, there's little sense of the city's powder-keg atmosphere.

Ron Shelton's skittish camera is forever changing angle, trying to spice up verbal confrontations that would play much better if he just let the actors go at it. The intention may be to unsettle, but ultimately it just irritates. As does the intrusive, clichéd, jazz score.

The star saves the picture. Sheldon Perry is a complex creation - a murderous bigot who thinks he's one of the good guys; a would-be champion of justice, who terrifies his wife and child. Russell gives the finest performance of his career, playing Sheldon straight and unselfconsciously, with no star smirks to camera. It's a fearless, brilliant piece of acting.

If "Dark Blue" lived up to its star's turn, it would be superb. As it is, it's an engaging, tough policier that's far from uniform but only a must-watch for genre aficionados.