The Invaders centered on David Vincent (Roy Thinnes), a man who had learned that aliens are plotting to take over the world. Because of this he became a fugitive, moving from place to place lest the 'invaders' catch him. The aliens had already infiltrated human society to a large degree; there were aliens in local police departments, the news media, the corporate world, even the government. Anyone could be an invader from outer space. Luckily their ability to take human form was somewhat flawed. As they had no hearts, they would have neither a pulse nor a heartbeat. Sometimes their form might be slightly imperfect, most often the pinkie finger would jut out awkwardly. Finally, their bodies would glow when in need of the regeneration required to keep their human shape. When an Invader was destroyed, his body went up on a cloud of red smoke, with nothing but ashes left behind.

The Invaders was one of the earliest shows produced by Quinn Martin's Q-M Productions (previously he had supervised The Untouchables). The series was created by Larry Cohen, the director of the 70's cult classic lt's Alive. Its inspiration perhaps came not from the 60's so much as it did the 50's: the concept behind The Invaders is reminiscent of Invasion of the Body Snatchers and any number of other alien invasion movies, in which aliens take human form in order to take over the world. At the same time, however, the series could well have drawn upon fears common during the Red Scare of the early 50's for inspiration. The Invaders is in some ways reminiscent of the 50's syndicated series I Lead Three Lives. In that series it was put forth that the Communists had either recruited or planted various individuals throughout American society - a premise similar to The Invaders.

The Invaders debuted as a midiseason replacement January 10, 1967, Tuesday night at 8:30. The Invaders' first season established it as a solid adventure series, albeit one whose plots generally fell into one of three broad categories. The first category of plots involved Vincent offering assistance to those somehow threatened by The Invaders. A second category of plots involved the invaders' efforts to silence Vincent. A third category of plots involved Vincent's efforts to get solid evidence of the invaders' presence on Earth.

With its second season the show slid in the ratings following its peak in September. In January the series was moved to a new time slot on Tuesday night, 10:00; there it fared no better and its ratings failed to improve. Its final episode aired September 17, 1968.

The failure of The Invaders was apparently due in a large part to its time slot. For most of its run it faced the indomitable Red Skelton Hour on CBS. Its move to 10:00 on Tuesday night hardly helped matters; there it faced the last half of NBC's Tuesday Night at the Movies. Against such competition, the show was probably doomed.

There were perhaps other factors in The Invaders' failure to capture the audience as well. In nearly every episode almost no one ever believed Vincent. When someone did believe him, they usually turned out to be an alien. This made the series rather predictable to a degree, and undermined Vincent's credibility-if no one on the show believed him, why should the viewer? This formula, in which no one ever believes Vincent, may then have driven viewers away with its utter predictability.

Despite The Invaders' short run, it has remained one of the best remembered adventure series of the 60's. The reason for this is perhaps because it was so different for its time. Most science fiction series, from Voyage to the Bottom of the Sea to Star Trek, possessed a good deal of optimism: a common theme was that man would not only survive, but would prevail. On The Invaders whether man would survive, let alone prevail, rested on the shoulders of only one man and later a small group of individuals. Too, it must be pointed out that prior to this no other series had ever dealt with the concept of alien invasion, event though the idea had been around for ages. (The idea would be explored further in the UK TV series UFO, among others.)