An organization called SHADO fights off aliens who are infiltrating Earth by disguising themselves as humans.

The Earth is threatened by an alien race who kidnap and kill humans and even animals and and use them for their body parts. In the year 1980 S.H.A.D.O. (Supreme Headquarters Alien Defence Organization), a highly secret military organization, is set up in the hope of defending the Earth from this alien threat. This organization operates from a secret location beneath the Harlington-Straker film studio in London. S.H.A.D.O. also has a base on the moon with Interceptors as well as an early warning satellite that detects inbound UFOs (called S.I.D.), and operate a fleet of submarines. General James Henderson and commander Ed Straker have a team of highly trained and well equipped females and males to battle the regularly incoming hostile UFOs.—Robert

After UFO, but, before Space: 1999, Gerry Anderson had hoped to re-boot UFO, with a new series - featuring the technical advances which had been made with such films as Star Wars, and Star Trek. This film (which is actually the first few episode's of that series cobbbled together) was made, in hopes of stirring up interest in the project. Unfortunately, a continuation of UFO was not to be, for various reasons. After the idea of relaunching a revamped UFO collapsed, it was decided to make a new series - but, focus on the iconic Moonbase (rechristened 'Moonbase Alpha', and also without the fabulous purple-haired women officers, including Dolores Mantez, who manned it). The Commander, John Koenig (Martin Landau), along with Alpha's Dr. Helena Russell (the still gorgeous Barbara Bain), and Prof. Victor Bergman (Barry Morse), along with many others became the focus. Instead of being a first-line in Earth's defence against the UF0's, the Moon was jettisoned out of orbit - hurled across the galaxy, due to the explosion of the nuclear waste dumps.—U.N. Owen