District 9 (15)

Forget Transformers, Terminator and the other expensive tosh disfiguring our cinema screens this summer. District 9 is a South African sci-fi B-movie that punches well above its weight even as it falls back on inspiration from major-league precedents. If David Cronenberg had been handed the script of Starship Troopers and told to keep the budget tight, it might have looked a bit like this.

One of the writer-director Neill Blomkamp's best moves here is to turn the stock idea of alien invasion on its head. This is his scenario: in the 1980s, a gigantic spaceship became stranded over Johannesburg, and its inhabitants, instead of launching a hostile attack, had to be relieved from their stricken craft and domiciled on earth. Being an unsightly race of crustacean-type bipeds – their derogatory nickname is "prawns" – they are herded away from humankind into a refugee camp known as District 9. Cut to the present, and the authorities have contracted a private company, MNU, to evict the aliens from what's become a slum township and relocate them to a concentration camp. In charge of this operation is a field worker, Wikus van der Merwe (Sharlto Copley), who fails to take precautions during the evacuation and becomes infected with alien DNA.

Up to this point, the historical allegory of District 9 is unignorable. Nobody actually mentions the word "apartheid", but the resonances abound. Caught between a private-contract army that break into their houses and an underworld of Nigerian gangsters who exploit them, the aliens face a system of oppression that inevitably calls to mind the imbecile cruelties of the South African police state. What transpires, however, takes the plot into the realm of nightmare: a hush-hush genetic experimentation program from which MNU will adapt the aliens' more powerful weaponry to their own use.

It's in this context that the film's choice of hero becomes especially interesting. Wikus begins the story as a joke, a nerdy bureaucrat playing up to the TV cameras as though he were the star of his own docudrama, and plainly incapable of exercising any proper authority. We find that he only got the job because his father-in-law is the head of MNU. Wikus's infection from the alien virus takes him through terror, despair and, finally, to resistance, as he joins forces with an alien scientist whose long-term plan has been to get back to the mothership. The reluctant alliance of running dog and underdog is itself a movie cliché, but it's given a lift by the unlikeliness of both partners – what kind of extra-terrestrial, after all, has a name like "Christopher Johnson"?

You can tick off the sci-fi references, from the heavyweights of Alien (naturally) and Blade Runner to parables of mutation such as The Fly, RoboCop and the film's producer Peter Jackson's no-budget horror Bad Taste. Yet the borrowings feel incidental: Blomkamp and his co-writer, Terri Tatchell, aren't interested in your movie knowledge, they just want to dazzle your eyeballs and frazzle your senses. Even in its last third, when the stalk-and-flee action cleaves to conventional models, the pace and exuberance never let up for a second. What's really surprising is the way Copley's performance as Wikus grows on you; the office twit is turned by his ordeal into a creature of pathos, and he manages this even while mutating into an outsize prawn.