In a dystopian near-future Los Angeles, a couple, Katie (Callies) and Will (Holloway) Bowman live with two of their three children under a regime of military occupation by an organization known as the Colony Transitional Authority. They are part of a larger invading force of extraterrestrial origin who are referred to as the "Hosts", and as the "Raps", apparently a reference to raptors (the logo of the human collaborating forces features a stylized bird of prey). It is said of them that "no one ever sees them". The Hosts have built an enormous wall, around 20–30 stories tall, several meters thick, and many miles in length, which surrounds the central part of Los Angeles, where the series is set. Other similar walls have been constructed around other major cities (now called "Blocs"), while various buildings still display severe damage from the armed conflict during the invasion, known as the "Arrival". The geographical extent of the alien invasion is unclear, but it is presumably worldwide. The occupying forces shown to the viewers are all human, and enforce their occupation via black-and-red-uniformed militarized police with automatic firearms and armored personnel carriers, nicknamed the "Redhats".
A privileged class of elites, the "Proxies", are drawn by the Hosts from the local population, and are denigrated by some residents of the bloc as collaborators. These forces maintain control by separation of loved ones, shoot-on-sight curfews, forced disappearances, random checkpoints and frequent electronic identity checks, limitation of motor vehicle usage to official transport by permit only (most citizens must walk or ride bicycles), pervasive visual propaganda, slave labor in a place called the "Factory" for transgressors (and their families) who are not executed and electronic surveillance with Host-provided drone aircraft that launch from the wall. Some medical problems, such as diabetes, have been "deemed unworthy for treatment" by the Hosts, to cull the population with a crude form of eugenics.
