Most significant of these is millionaire industrialist Edgar Scoville (Kent Smith), who became a semi-regular character as of December 1967, heading a small but influential group from the episode "The Believers".

In "Moonshot", the NASA official (Peter Graves) is fully expecting Vincent to arrive; and in "Condition: Red", a NORAD officer and staff witness an alien UFO formation onscreen, and are left convinced.

The emphasis of the series is on Vincent and his efforts, and unlike most science fiction the back story of the aliens—their "dying" planet in "another galaxy" (or even their names)—is "a deliberate blank".

[3] Unless they receive periodic treatments in what Vincent calls "regeneration chambers", which consume a great deal of electrical power, they revert to their alien form.

To kill humans they apply a small, handheld, disc-shaped weapon with five glowing white lights to the back of the victim's head or neck to induce a seemingly natural death, which is usually diagnosed as a cerebral hemorrhage.

Also in their arsenal is a small device consisting of two spinning, transparent crystals joined at their corners which acts like a truth serum, forces human beings to do the aliens' bidding, or (in most cases) imposes the complete loss of memory of previous events.

[2] The large numbers of UFO reports in the post-World War II era was the subject of paranoia and conspiracy, as scientists and authorities (the Condon Committee and the Robertson Panel), and debunkers dismissed or downplayed the reports;[Note 1] and dedicated "ufologists" made sometimes-outlandish claims of alien presence on Earth and of earthly conspiracies to suppress evidence of it.

Chuck Connors starred in Branded (1965) as a soldier court-martialed for cowardice, who traveled the West searching for witnesses and proof that he had acted valiantly, and Coronet Blue (1967) about Michael Alden, a man suffering from amnesia who was being pursued by a powerful group of people.

Also typical of Quinn Martin productions of the time, the show was divided into "Acts" labeled by the Roman numerals I-IV, preceded by a cold open.

The fireball is seen by rancher and ex-nurse Gale Frazer (Barbara Barrie), who drives up to the crash site just as the one surviving alien Blake (Richard Anderson) vaporizes the saucer in a red glow.

In New Jersey, Charlie Gilman (Don Gordon), an old Korean War Army friend of Vincent's, stands accused of murdering Fred Wilk, whose body has vaporized following a fight between them near an open incinerator.

After wandering some distance, he encounters some student geologists with their professor Dr. John Devin (William Sargent), who tells Vincent that he is in Bowman County, North Dakota.

As the summit commences in a Baltic state from where the "AR5" will be launched aboard a missile, David Vincent and Michael Tressider (William Windom) arrive and catch up with Ellie (Diana Hyland).

David Vincent arrives at an evangelical meeting in Bakersfield, California to investigate a "prophet" who apparently glows red in a fashion similar to that of dying aliens.

When Vincent divulges that he has a backup set of scans he is brought to the airport next day by a bogus alien taxi driver who tries to swap David's luggage.

When Vincent arrives at the office again, he meets the real professors, but is immediately suspicious of Crowell's daughter Laura (Sally Kellerman) when he notices a suspicious-looking scar over her right fifth metacarpal.

David Vincent has finally gathered some serious support in his quest to stop the invaders in the form of industrialist Edgar Scoville (Kent Smith).

In Vermont, David Vincent is summoned by a Bob Torin (Anthony Eisley) who has seen strange alien activity at an abandoned ski lodge.

As Vincent and Torin travel back to Washington they take a break at a motel and David calls Edgar Scoville (Kent Smith).

Scoville tells Vincent to take the alien leader to Belding Army Base and to ask for Colonel Gentry (John Graham).

At the behest of Bob Ferrara (John Lasell), who is one of the group of seven believers, David is meeting publishing magnate William Mace (Martin Wolfson) and his secretary June Murray (Nancy Kovack) in New York City.

Meanwhile detectives under lieutenant Connors (Ken Lynch) have arrived on the scene of Kramer's death and when they catch up with David decide to hold him for questioning.

When an unknown lawyer has David released, Vincent finds that he has been fired from a building project owing to the bad publicity surrounding the Kramer accusation.

At the highly secretive Slaton Research Center in New Jersey, Professor Julian Reed (Charles Aidman) appears to be paranoid about the presence of aliens and falls from a balcony apparently running from delusional thoughts.

At the behest of journalist Mike Calvin (Chris Robinson) David Vincent arrives to meet him at the docked vessel only to discover that the evidence has already been removed.

Scoville arrives to meet Calvin and to search for David who has been taken by Mob leader Peter Kalter (J. D. Cannon) who is just interested in recovering his shipment of narcotics.

David Vincent arrives to investigate the shrine and the sleepy town and lands at the bar where Beth's father Harry (Edward Asner) has the crystal on display and being gazed lovingly upon by a few locals.

Hatcher needs more evidence, and his case is conveniently strengthened when a certain Dr. Stanley Frederickson (Robert H. Harris), arrives claiming that he is one of the believers but will be happy to testify against them.

In the plot of that final episode of the series, the saucer was a prisoner transport ship of the future operated by humans that malfunctioned and crashed on Earth at night in the heavy vegetation of a jungle.

Several episodes aired in Hungary in 1980, running from July 4 to September 5 under the title Támadás egy idegen bolygóról ("Attack from an Alien Planet").