On a council estate in South London, a teenage street gang, led by the tough and resourceful Moses, finds themselves defending their turf against an unusual threat on Guy Fawkes Night. Their ordinary routine of mugging and intimidation takes a turn for the extraordinary when a meteorite crashes nearby, unleashing a ferocious alien creature. The gang kills the creature and, seeing an opportunity for notoriety, they take its carcass as a trophy. However, their victory is short-lived when more meteorites begin to fall, bringing with them more of the savage extraterrestrial beings, which are larger and more menacing than the first.

As the estate becomes a war zone, the gang's initial bravado turns to desperation, and they are forced to retreat into the block - the very building they usually preside over with intimidating control. Amidst the chaos, they reluctantly team up with Sam, a nurse whom they previously mugged, showing that the alien invasion is a great leveler, blurring the lines between the attackers and the victims. Together, this unlikely group must use their knowledge of the block and every resource they can scavenge to survive the night against an escalating alien onslaught, defending their home against an enemy far stranger and more deadly than any rival gang.