A massive alien spaceship arrives on Earth and hovers, apparently weightless and effortless, over Johannesburg, South Africa. When nothing further happens, humans, with the aid of helicopters, fly up and cut their way into the ship with blow torches. They find aliens helpless and starving. The ship is huge, as large as a city. There are millions of aliens. They look insectoid, about seven feet tall, two arms with claws, a head with two eyes, feelers around the mouth orifice and antennae on top of the head. The legs have several additional joints, making the creatures look very unhuman. The humans call the aliens Prawns, due to their similarity to giant shrimp or lobster.
The humans bring the aliens down to a concentration camp, or rather a slum, called District 9, where the aliens live in squalor. Decades go by. The ship hangs over the city and becomes a permanent fixture, abandoned, unchanged, apparently without power. The aliens have children, go about their business surprisingly like human slum dwellers would live outside Calcutta or Rio. They are forbidden to have weapons, technology or open commerce. The humans have confiscated their weapons, which appear far superior to human weapons, but are connected to alien DNA, rendering them useless to humans, authorities and thugs alike.
Decades go by. The humans learn to sort of understand the language (clicking and chirping) of the aliens, and the aliens understand English. The South African authorities are trying to get the aliens to move from District 9 further out to District 10. The hapless hero Wikus van der Merwe (Sharlto Copley) is put in charge of this operation, and he seems not quite ready for the job. In addition, the aliens don’t really want to move. Conflicts arise and things escalate.
Here are credible, believable aliens. Humans see them, but do not understand them. Communication is difficult. Understanding of motives is almost impossible. Aliens stranded on Earth are helpless, just like humans would be on some other planet. Living conditions are miserable, just like human living conditions on some other planet would likely be. The aliens can breathe our air — well, that was necessary for the movie to work.
Watching District 9 took me back to watching 1950ies science fiction thrillers with aliens. But these were realistic, not at all humanoid, and the conditions as well as the human responses were credible. After a while, no matter how disgusting and revolting the aliens looked at the beginning, I started getting used to them and sympathizing with them. I wanted them to succeed and I wanted the human profit apparatus, organized crime and government ineptness to be defeated. I rooted for the aliens.