“City of Men” takes place in a Rio favela, or shantytown, where children are cast adrift at a young age and left to grow up on their own. Produced by “City of God” director Fernando Meirelles, Paulo Morelli’s follow-up to that filmmaker’s Oscar-nominated 2002 film, “City of Men,” depicts the same kind of brash, impoverished hillside community — a gang-ruled honeycomb where the air is noisy with squawking stereos and barking dogs. Mr. Morelli’s film is a vivid and believable portrait, albeit somewhat overstuffed. In this case, that soundtrack is no match for the cacophony of intersecting dramas that take over the screen.

There are two main stories here, both of which address themes of friendship and loyalty. As his 18th birthday approaches, Wallace (Darlan Cunha) goes in search of the father he has never known. Wallace and his footloose pal Ace (Douglas Silva), whose own father was killed many years before in a holdup, track the man down just as he is being released from prison. But Heraldo (Rodrigo dos Santos) doesn’t seem entirely eager to reconnect with his son.

Meanwhile, a gang war is brewing. A scowling tough named Fasto (Eduardo Piranha) betrays the local honcho, Midnight (Jonathan Haagensen), and as word spreads that Fasto is plotting to return to Dead End Hill with new allies and firepower, scared residents prepare for the worst.

Wallace’s girlfriend (Naima Silva), whose brother has joined ranks with Fasto, has her house trashed and her head shaved by Midnight’s gang. Wallace, who is Midnight’s cousin, flees the hill. Ace is without any particular allegiance, but gets branded as a Midnight partisan after being in the wrong place at the wrong time. Everyone else tries to avoid getting caught in the crossfire.

There are several other subplots, and everything collides bloodily — and Adriano Goldman’s handheld cinematography turns darker — in the film’s harrowing climax, when the gangs bring their grudge to the streets. As in “City of God,” the underage killers roaming the favela struggle to hold a gun properly — but rarely hesitate to pull the trigger.

Mr. Morelli abstains from too much showy editing or camerawork, and shoot-outs and samba parties are not filmed, as they were in “City of God,” with the kind of rambunctious verve that draws comparisons to “Goodfellas.” This earnest depiction of Rio’s slums often feels like a documentary, with Mr. Morelli and screenwriter Elena Soarez leaving little room for colorful characters that loom larger than life.

Unfortunately, the film’s impact is dulled by the jostling story lines. “City of Men” grew out of a wildly popular Brazilian TV show of the same name that was later picked up by the Sundance Channel, and the film’s thick mix of characters surely played out better in serial form than it does in this 110-minute format. Perhaps aware of this, the filmmakers boost the tempo in an effort to cram everything in. But the pace at times seems unjustifiably hurried, and it becomes hard to keep track of who’s who. That’s a shame, because the naturalistic performances are topnotch, and the film shows an impressive command of the relationships that govern the tight but precariously knit community. (Messrs. Silva and Cunha, both of whom grew up in favelas and acted in “City of God” and the “City of Men” TV series, undoubtedly deserve some of the credit for this.) The film never gets boring, and benefits from some wonderfully spontaneous details, as when a tiny-legged stray dog loses its footing on the favela steps. This Rio shantytown, where fathers leave their offspring to go kill one another and the brief glory of gang membership beckons, is a slippery slope. Despite its overstretch, “City of Men” does manage to convey a place where deprivation makes men out of children, and vice versa.