The film was produced by Michael Deeley and Barry Spikings, who reunited two years later to work on The Deer Hunter. Despite a mixed critical response upon release, the film is now considered an important work of science fiction cinema and one of the best films of Roeg's career.
Thomas Jerome Newton is a humanoid alien who comes to Earth from a distant planet on a mission to take water back to his home planet, which is experiencing a catastrophic drought. Throughout the film are brief sequences of his wife and children back on his home planet, suffering, perhaps dying.
Newton uses the advanced technology of his home planet to patent many inventions on Earth, and acquires tremendous wealth as the head of a technology-based conglomerate, World Enterprises Corporation, aided by leading patent attorney Oliver Farnsworth. His wealth is needed to construct a space vehicle with the intention of shipping water back to his home planet. While revisiting New Mexico, he meets Mary-Lou, a lonely, unloved, and simple girl who works as a maid, bell-hop, and elevator operator in a small hotel; he tells her he is English. Mary-Lou introduces Newton to many customs of Earth, including church-going, alcohol, and sex. She and Newton live together in a house Newton has built close to where he first landed in New Mexico.
Meanwhile, Dr. Nathan Bryce, a former womaniser and college professor, has landed a job as a fuel technician with World Enterprises and slowly becomes Newton's confidant. Bryce senses Newton's alienness and arranges a meeting with Newton at his home where he has hidden a special X-ray camera. When he steals a picture of Newton with the camera, it reveals Newton's alien physiology. Newton's appetite for alcohol and television (he watches multiple televisions at once) becomes crippling and he and Mary-Lou fight. Realizing that Bryce has learnt his secret, Newton reveals his alien form to Mary-Lou, and her resulting reaction is one of pure shock and horror. He leaves her.
Newton completes the spaceship and attempts to take it on its maiden voyage amid intense press exposure. However, just before his scheduled take-off, he is seized and detained, apparently by the government and a rival company; his business partner, Farnsworth, is murdered. The government, which has apparently been told by Bryce that Newton is an alien, holds him captive in a locked luxury apartment, constructed deep within a hotel. During his stay, they keep him sedated with alcohol (to which he has become addicted) and continuously subject him to rigorous medical tests – notably one involving X-rays which causes the contact lenses he wears as part of his human disguise to permanently affix themselves to his eyes.