The architect David Vincent accidentally learns of a secret alien invasion already underway and thereafter travels from place to place attempting to foil the aliens' plots and warn a skeptical populace of the danger. Ot… See more

According to producer Alan A. Armer, "The major thing that the show had going for it is the fact that we are all a little bit paranoid, and that it’s easy to identify with ... one person fighting the society, fighting the governmen… See more

• Roy Thinnes appears as David Vincent in all 43 episodes. For the first 30 episodes, he is the only recurring character.
• Kent Smith appears as Edgar Scoville for 13 episodes, beginning with episode 31, "The Believers". … See more

The series was produced by Quinn Martin, who was looking for a show to replace the immensely popular The Fugitive, which was ending its run in 1967. Larry Cohen, the series' creator, had conceived two earlier series with … See more