The Puppet Masters

In 1951, Robert Heinlein published his award-winning science fiction masterpiece, The Puppet Masters in which American secret agents detect (and ultimately overcome) parasitic invaders from outer space.

Sam (not his real name) wakes up to the jarring alarm of his skull phone. He's ordered to report to the Old Man personally, for the emergency is that a space ship his landed in Grunnel, Iowa. The Section sent in several agents, but none came back; and they only got one fragmentary report: "They are little creatures, about --" (before the sound cut off).

The Old Man risks the entire Section by going out in the field himself, along with a female agent he hadn't met before. He tells Sam and Mary to put on a brother and sister act; he plays the slower of two not-too-bright country bumpkins out seeing the sights with an elderly relative (the Old Man).

They encounter vaguely round-shouldered people, and Mary notices that the men aren't sexually attracted to her, which means that these men are obviously hag-ridden by parisitic slugs! The invaders have taken over their brains and nervous systems and control earthlings like a puppet master controlling a marionette!!

Sam and the Old Man try vainly to convince the President of the United States about the menace but are dismissed. "Don't worry, the republic won't fall apart." So Sam forces his way into a TV executive's office intending to capture a parasite on live video (portable VCRs hadn't been envisioned in the 1950s) but a blown tube ruins the shot, and the President tells the Old Man to fire Sam.

Meanwhile, the invaders are multiplying, and no one will believe it. Apparently licked, the Old Man flies to Florida to lie on the beach and wait for the world to go to hell. But, wait! Sam has an idea . . .