The Invaders was a wonderful show. Roy Thinnes played architect David Vincent. One night, he stumbled upon an alien craft landing. Aliens had come from a dying world to take over the Earth. What should Vincent do? Contact the Air Force and get them to kick butt?
Actually, no, Vincent was alone on this one which is what made this show great. The authorities didn't believe him, in fact no-one did. Whenever an alien was killed, he/she would vaporize. At first, there was no way of knowing who to trust; anybody could be an invader, the Invaders could take over anyone. Of course, later on we learned that the aliens had a funny little finger even when in human form.
Like most films and shows of the 1950's/60's, the Invaders was about paranoia. No-one could trust anyone. Vincent could never be sure that potential allies were not really invaders themselves. He tried in vain to convince people but he was fighting a losing battle. The great thing was that he was alone in his battle. It was a great-if depressing-show.
One of the other things worth mentioning is that there are viewers who suspected that Vincent was actually an invader himself and had been placed on Earth and told to try and convince the population of the danger. Apparently, the invaders used him to test the likelihood of their discovery. Is it true? Your guess is as good as mine.