Alfred Hitchcock said that a film is not a slice of life, it's a piece of cake. The brilliant District 9, with its faux documentary style and raw South African township setting, might look like a slice of life, but what you get for your money is a juicy science fiction gateau with a bloody cherry on top.

District 9 takes the creaky old premise of alien invasion and turns it on its head. There's a giant mothership hovering ominously in the sky, but it's over Johannesburg rather than the White House. Instead of raining down fire, the ship is basically broken, and far from proffering eternal wisdom, the aliens within are pathetic, malnourished refugees.

The new arrivals are an embarrassment to the South African government, which promptly confines them to a shanty town that looks an awful lot like Soweto. There, they are subject to hatred and racial abuse (the locals call them "prawns" for their crustacean appearance) and ruthlessly exploited by petty gang lords, who barter their unusable technology for cat food.

Into this squalid mess steps Wikus Van De Merwe (Sharlto Copely), a hapless middle manager for the evil Multi National United corporation. Charged with forcibly relocating the ETs to a new camp out of town, Wikus suffers a close encounter with some disgusting alien goo that leaves him with a lobster claw for an arm. Unfortunately for him, this makes Wikus the only human being capable of operating Prawn weaponry, and his former bosses will stop at nothing to get him onto the dissection table.