The Puppet Masters is a novel by Robert A. Heinlein about an Alien Invasion, first published in 1951. This was the only novel Heinlein published on the subject and he cemented most of the tropes usually associated with invasion stories.Secret agents Sam, Mary and "The Old Man" fight a fantastical battle against parasitic aliens who are bent on assimilating all of humanity and taking control of Earth. Danger is everywhere when anyone around you could be a host.
Alien Abduction: The aliens have been abducting humans for years, possibly centuries, as part of the plan to conquer Earth. It turns out that the protagonist's Love Interest was abducted from a human colony on Venus as a child; this provides a key to the eventual defeat of the invasion.
Chickification: Mary is a secret agent who carries an excessive amount of firepower and is certainly willing to use it. After marrying Sam halfway through the book, she becomes an instant "Yes dear" housewife, though it's unclear whether this is Values Dissonance on Heinlein's part or if he's just playing the situation for its humorous aspects.
Easily Thwarted Alien Invasion: The solution is reached by logical reasoning rather than detailed research or military strategy, and turns out to be relatively simple.
Embarrassing First Name: Sam goes through several false identities. Only late in the novel does he go right up to his father and asks, "Dad, why did you name me Elihu?"
Exposition Intuition: Mary. Her intuition helps her to distinguish infected humans from non-infected ones. The author never explains how is she able to do it, though it is implied that this is somehow associated with sexual arousal as something of which only humans are capable.
The Secret Service guards gave us the works. An X-Ray went beep! and I surrendered my heater. Mary turned out to be a walking arsenal; the machine gave four beeps and a hicough, though you would have sworn she couldn't hide a tax receipt.
During a later strip-search he mentions that Mary "added considerably to the pile of hardware. I decided she just plain liked guns."
Flying Car: It's past 2007 and we still don't have them!
Hello, Nurse!: A metal neckline and a white sash across her breasts is everything which the nurse taking care of the main character wears up from her waistline.
Heroes Want Redheads: Sam and Mary, though it's not clear whether the red color of Mary's hair is natural or not.
If You Won't, I Will: Sam is asked to allow one of the title monsters to take control of him as an experiment. He refuses, and discovers that his girlfriend Mary has volunteered to do it and will be going in his place. He reverses himself and agrees to take part.
It's Personal: Things really get personal for Sam when his beloved cat Pirate dies after being infected. He mentions his need for revenge in the closing of the book.
Re Cut: As with several other Heinlein books, The Puppet Masters was released in an expanded edition by his wife Virginia after his death. Most of the added material is graphic violent/sexual content censored at the time of the original release.
Science Is Bad: While the scientific method is acceptable — even praiseworthy — when used to combat the Puppet Masters, science-for-science's sake is scorned by the main characters. The feeling is that pure scientists don't actually produce anything useful, unlike engineers.
The novel was published in 1951 and set in 2007. Although the heroine is just as tough and capable as the male lead (sometimes more so), the moment gender roles or romantic relationships come up she turns, hilariously, into June Cleaver.
People complained about having to walk around bare to the waist (or in bikini tops for women) far more in the book than they probably would have in real life 2007.
Space Elves: They are the race which the aliens apparently exploit on their home planet. Supposedly, they were the original inhabitants of Titan.
Spreading Disaster Map Graphic: A map is used to show the extent of parasite infestation in the U.S., with areas controlled by the parasites glowing red, those under human control in green, and contested areas in amber. Several times the red areas of the map are described as expanding, showing a spread of the parasites.