Modern urban crime movies typically follow one of two paths. They’re either dark and hyper realistic, like director John Singleton’s previous film “Boyz n the Hood,” or stylish crime fairy tales like “Snatch” and Tarantino’s “Reservoir Dogs” or “Pulp Fiction,” set in an underworld where the crooks are cool, violence is ever present and the far-off non-criminal world rarely intersects with the fantasy. Straddling the line between the two is Singelton’s latest film, “Four Brothers.”

The Mercers are the four brothers of the title: Bobby (Mark Whalberg), Jeremiah (Andre Benjamin), Angel (Tyrese Gibson) and Jack (Garrett Hedlund) are a motley, mixed-race crew of troubled foster kids who were raised by the saintly Evelyn Mercer (Fionnula Flanagan). The brothers are reunited on Thanksgiving after their mother is killed in what looks like a liquor store robbery gone bad. But the boys, battle-scarred veterans of Detroit’s crime-ridden streets, sense something’s hinky and proceed to blast their way through the city’s gangs in search of answers.

“Four Brothers” succeeds in the familiar, playful chemistry that the four brothers share. Despite the obvious age and racial differences between them, it’s not a stretch to believe that their bonds run deeper than sharing the same foster mother. During an early scene that takes place on Thanksgiving morning, the brothers wrestle, cook dinner and mourn the loss of their mother together. Later, Angel, Bobby and Jack hold an impromptu meeting in the bathroom, a bizarrely intimate conversation that anyone who grew up with siblings or had to share a dorm bathroom in college could easily appreciate.

This self-contained familial world contrasts sharply with director John Singleton’s vision of Detroit, full of gray industrial landscapes and crumbling buildings. It seems such a gritty, real place that the outlandish escapades of the Mercer family seem cartoonish, belonging more to the world of “Reservoir Dogs” than “Boyz.” During one of the film’s big action sequences, a small army of local thugs brandishing heavy artillery storm the Mercer home. The neighborhood is filled with machine gun fire as three of the four boys fight back, ending the siege with minimal effort. When the cops show up later, Lt. Greene (Terrance Howard), the only honest cop in the city—who also just happens to be investigating Ma Mercer’s death—tells the brothers he’ll chalk it all up to self-defense. I don’t know much about inner-city crime, but there’s no way a full-scale machine gun battle in a Detroit suburb could be dismissed as “self-defense.”

And for all their likable characteristics, there’s a lot about the Brothers Mercer that rings false. After deciding to tear up the Detroit underworld looking for mom’s killer, Bobby and Angel waste no time busting heads, pointing guns and dumping gasoline on people. It all goes well in that slightly dark, slightly cool tone that so many modern crime films adopt, until Bobby and Angel find the pair of hired guns that did the deed. After running the assassins off the road, the brothers climb out of their car and put two shots in each killer’s head, execution style. It wouldn’t have left such a bad taste in my mouth if the Mercer boys at least acknowledged the tension between their departed mother’s saintly, non-violent ways and their present crime spree. But there’s no recognition, no remorse, just a lot of gleeful vengeance for a woman who, in her brief moments on screen, seemed to have no use for the old “eye for an eye” concept.