Mill Valley, Marin County, California.

Dr Miles Bennell has lived there all his life. But one day Miles sees a patient who claims her Uncle isn't himself. He's a different person, despite being identical in every way except one: he is only pretending to have emotions.
Miles dismisses this as delusions and refers her to a psychiatrist.
Then he finds the pods. Giant seed pods, filled with a strange, grey substance. A strange grey substance that can slowly, slowly, become a perfect replica of a person.
But what has happened to the people being replicated?

Adapted for screen multiple times, The Body Snatchers is the origin of the phrase 'pod people', and a staple of pulp science fiction. Read by many as an allegory for the Cold War, or McCarthyism, it perfectly encapsulates the paranoia that comes with not knowing who around you can be trusted.