The year is 1980 and Earth is secretly under attack from Aliens who are harvesting human body parts in order to save their own race. To stop this menace, a secret organization known as SHADO, or Supreme Headquarters Alien Defence Organization, is formed to defend the Earth from the attacks.
SHADO consists of a Moonbase with fighter spacecraft to intercept the aliens before they get to Earth, a SkyDiver submarine with a launchable fighter should they get by the Moonbase, and various ground based assault vehicles should they get by all the other Earth defences.
The SHADO operations are coordinated from a movie studio front, known as Harlington-Straker studios. Underneath the movie studio grounds lies a vast operational complex run by the man in charge of the organization, Commander Ed Straker.
When a woman awakens from a ten year coma, she gives vital information about a alien encounter she had in an old abandoned farmhouse. Straker must make sense of her memories in order to unearth the terrifying UFO threat that has lain dormant since she lapsed into her coma.