A race of aliens arrive on Earth in a fleet of 50 huge, saucer-shaped motherships, which hover over major key cities across the world. They reveal themselves on the roof of the United Nations building in New York City, appearing human but requiring special glasses to protect their eyes and having a distinctive resonance to their voices. Simply referred to as the Visitors, they reach out in friendship, ostensibly seeking the help of humans to obtain chemicals and minerals needed to aid their ailing world. In return, the Visitors promise to share their advanced technology with humanity. The governments of Earth accept the arrangement, and the Visitors, commanded by their leader John and his deputy Diana, begin to gain considerable influence with human authorities.
However, strange events begin to occur. Scientists become objects of increasing media hostility, and experience government restrictions on their activities and movements. Others, particularly those keen on examining the Visitors more closely, begin to disappear or are discredited. Noted scientists confess to subversive activities; some exhibit other unusual behavior, such as suddenly demonstrating an opposite hand preference to the one they were known to have.
Television journalist cameraman Michael Donovan covertly boards one of the Visitors’ motherships and discovers that beneath their human-like facade, the aliens are actually carnivorous reptiles – preferring to eat live food, like rodents and birds. Donovan records some of his findings on videotape and escapes from the mothership with the evidence, but just as the exposé is about to air on television, the broadcast is interrupted by the Visitors who have taken control of the media. Their announcement makes Donovan a fugitive, pursued by both the police and the Visitors.
Scientists around the world continue to be persecuted – both to discredit them (as the part of the human population most likely to discover the Visitors’ secrets) and to distract the rest of the population with a scapegoat to whom they could attribute their fears. Key human individuals are subjected to Diana’s special mind control process called “conversion”, which turned them into the Visitors’ pawns, leaving only subtle behavioral clues to this manipulation. Others become subjects of Diana’s horrifying biological experiments. However, some humans (including Mike Donovan’s mother, Eleanor Dupres) willingly collaborate with the Visitors, seduced by their power. Daniel Bernstein, a grandson of a Jewish Holocaust survivor, joined the Visitor Youth and begins to reveal the locations of traitors to the alien cause. One teenager, Robin Maxwell, the daughter of a well-known scientist who went into hiding, has sex with a male Visitor named Brian, who impregnates her as one of Diana’s “medical experiments”.
A resistance movement is formed, determined to expose and oppose the Visitors as much as possible. The Los Angeles cell leader is Juliet “Julie” Parrish. Donovan later joins the group and, again sneaking aboard a mothership, he learns from a Visitor named Martin that the story about the Visitors needing waste chemicals was a false story. The true purpose of the Visitors’ arrival on Earth was to conquer and subdue the planet, steal all of the Earth’s water, and harvest the human race as food, leaving only a few as slaves and soldiers/cannon fodder for the Visitors’ wars with other alien races. Martin is one of many dissidents among the Visitors (later known as the Fifth Column) who oppose their leader’s plans. Martin promises to aid the Resistance, and gives Donovan access to one of their sky-fighter ships, which he quickly learns how to pilot.
Soon, the members of the Resistance strike their first blows against the Visitors, while procuring laboratory equipment and modern military weapons from National Guard armories to carry on the fight. The symbol of the resistance was a blood-red letter V (for victory) spray-painted over posters promoting Visitor friendship among humans.
The mini-series ends with the Visitors now virtually controlling the Earth, and the resistance sending a transmission into space to ask for help from other alien races who can help them defeat the Visitors.