One of the best episodes of "Star Trek: The Next Generation" was from the end of season one. In "Conspiracy" an alien life form invades folks and turns them into robots to do the monster's bidding. The only obvious evidence of the alien infestation of a person was a tiny protrusion on the neck. Well, although a very good show, it was hardly original as the idea was also done in "The Monster From Outer Space"....and even earlier than this with the film "The Invasion of the Body Snatchers".
When "The Monster From Outer Space" begins, NASA is following a space capsule on its way to re-entry. Unfortunately, some sort of alien life form is attached to it and the NASA folks THINK they've burned it off on re-entry. But this isn't the case, and the weird creature survives. The Seaview is sent to pick up the capsule and they discover a now larger and scary monster at the bottom of the sea*. They mostly seem interested in driving it away instead of destroying it...something that makes no sense at all. Well, the idiots from the Seaview assume all is well and bring the capsule aboard....and learn that hard way that the creature is nearly unstoppable!
While much of the show is a bit silly, the basic idea of an alien force taking control of people and turning them into its pawns is pretty cool. And, there are many moments of the show I enjoyed...and is well worth seeing...even in spite of a few dumb scenes (such as two men holding everyone off with a hose...and the baddies all have guns!).
*While the monster is hillariously dumb by modern standards, you have to take into account two important things. First, an average TV episode of the era was budgeted at about $60,000 (more or less). That didn't leave much room for special effects plus salaries plus everything else. Second, because CGI is so convincingly and seamlessly done today, there is a tendency to laugh at stuff made before the era of computer generated effects. For 1965, the monster is silly but probably about the best they could do.