Teenage thugs patrolling a grim council estate in south London are stunned when flaming asteroids begin to drop from the sky and disgorge space aliens who look like eyeless black bears with concentric rows of green, glow-in-the-dark fangs. This low-budget sci-fi item was produced by some of the Brits who made Shaun of the Dead and Hot Fuzz, including their writer and director, Edgar Wright, but it hardly compares, despite Nick Frost’s brief appearance as a mangy pot dealer. John Boyega, in his screen debut, gives a serviceable performance as a cool Jamaican gang leader who battles the vicious aliens, and Jodie Whittaker plays a young nurse who comes to his aid even though he’s mugged her in the opening scene. Joe Cornish directed his own script, which suffers from thin characterization, weak dialogue, and a confused ending; we never do find out where the beasts came from, what they wanted, or whether the extraterrestrial attack is even over.