Available on DVD: “Attack the Block”

John Boyega (center) leads his teen gang in Attack the Block

"This is the block," declares one of the adolescent heroes of Attack the Block. "We take care of things our way." Set entirely within a tenement apartment building ("the block") and the surrounding South London projects, the movie follows five young teens (John Boyega, Alex Esmail, Franz Drameh, Leeon Jones and Simon Howard) on one night as they embark on a typical regimen of criminal mischief and mayhem — until ferocious, snaggle-toothed aliens start falling from the sky, forcing the boys to take up arms against the invaders and protect their turf.

When seen under bright lights, the extraterrestrials resemble the unfortunate offspring of a gorilla and a wolf. For most of Attack the Block, though, the otherworldly visitors are simply dark silhouettes with glowing eyes and teeth. They almost look like cartoons, but they serve the necessary purpose, the way that big rubber shark did its duty in Jaws. The primary concern of Attack the Block isn’t cutting-edge special effects: The movie is more interested in making viewers consider its disenfranchised protagonists from a fresh perspective. The fact that the film accomplishes this without a trace of gooey sentimentality is a small miracle. When characters die, and several likable ones do, you feel the sting of their death. But the movie — like these scrappy, street-smart kids — never lingers on schmaltzy emotions. It just moves on to the next crisis.

As much of a comedy as a mean little sci-fi/horror picture, Attack the Block defies categorization. Everything about this low-budget Sundance hit grows on you, from the delinquents we first meet while they’re mugging a female nurse (Jodie Whittaker) to the thick accents and slang that initially render the dialogue unintelligible (your ears become used to them, though). With his debut, writer-director Joe Cornish (who also co-wrote the screenplay for the Steven Spielberg/Peter Jackson collaboration The Adventures of Tintin) displays a knack for deft characterizations and action choreography. In one of the film’s best scenes, the five boys, who have now joined forces with the nurse they had previously robbed, seek shelter inside the apartment of two girls who don’t want to be bothered and aren’t putting up with this nonsense. When the aliens suddenly attack, though, the girls prove to be just as tough and resourceful as the boys: Everyone here is a product of their environment.

Attack the Block is often reminiscent of Shaun of the Dead, another British import that successfully melded laughs with scares (the presence of Shaun’s Nick Frost here as a marijuana dealer cements the connection). But Cornish has bigger aspirations than a mere love letter to a beloved genre: Here is a shaggy monster movie that pulls double-duty as a satire of class and ethnic barriers, and how those barriers quickly disappear when we are forced to fight for our simple survival.