"We can't bring her back, but we can send her some company!" says Bobby Mercer (Mark Wahlberg), the oldest of the Four Brothers seeking revenge for their mother's gangland murder in John Singleton's violent thriller. Resembling a more mature spin on his 1991 debut Boyz N The Hood, this dark melodrama is notable more for its bold colour-blind casting than for its workmanlike narrative, which swiftly dissolves into a litany of brutally sadistic acts knotted together by a feeble whodunnit plot.

When Evelyn Mercer (Fionnula Flanagan) is killed during a grocery store hold-up, the police chalk her up as another victim of Detroit's escalating crime wave. But hothead Bobby and his three adoptive siblings - ladykiller Angel (Tyrese Gibson), family man Jeremiah (André Benjamin) and rocker Jack (Garrett Hedlund) - think otherwise. ("It wasn't no gang shooting, it was an execution!" Bobby fumes.)

"TEDIOUSLY ROUTINE"

Battering, maiming and torturing their way through the city's seedy underworld, they soon realise their mom's death was down to ruthless hoodlum Victor Sweet (Chiwetel Ejiofor). Outgunned and outnumbered, though, they'll need to stick together if they're to bring him to book.

Once you get past the novelty of its racially diverse central quartet, Singleton's dull, sluggishly paced actioner feels tediously routine as its bickering heroes get closer to their quarry. The fact that they also get closer to each other allows some flickers of human interest to punctuate the mayhem. Alas, these come with a dollop of sickly sentiment that makes this formulaic movie even more unpalatable.