In an alternative 1982, an extraterrestrial spaceship appears over Johannesburg, South Africa. After hovering inactive for months, human authorities cut their way into the ship and discover a multitude of malnourished and leaderless alien refugees. These beings, derogatorily referred to as "prawns," are subsequently confined to a government camp on Earth called District 9. As international pressure to address the alien issue mounts, control of District 9 is handed over to Multi-National United (MNU), a private company with interests in exploiting the aliens' advanced technology. However, their technology is unusable by humans, functioning only when operated by alien DNA.

Twenty-eight years later, the situation has deteriorated, with District 9 turning into a militarized slum. The human populace grows increasingly intolerant of the alien presence, giving rise to violence and unrest. MNU agent Wikus van de Merwe is assigned the task of relocating the aliens to District 10, a new camp situated further from human residential areas. During the eviction process, Wikus experiences a life-altering incident involving alien technology, which begins to transform him in unprecedented ways. This incident draws the interest of the aliens and MNU alike, leading him to forge an unlikely alliance with an alien named Christopher Johnson, who has his own agenda. The bond between Wikus and Christopher develops amidst the backdrop of political, social, and corporate machinations, challenging the status quo of human-alien relations.