fter centuries of hushed-up rumors about flying saucers, the newscasts are talking about a spaceship landing in Iowa. But even as Sam, an agent for a secret shadow intelligence organization, is making for the scene with his boss and Mary, his shapely female colleague, the newscasts correct themselves: It was all a hoax by a couple of farm boys. The agents, suspicious, visit the TV station that originated the story. They discover to their horror that the people there are possessed by sluglike aliens-- parasites that adhere to their victims' backs and control their every thought.
Sam's boss, the Old Man, knows that the only way to contain the threat is swift government action, but the president isn't convinced until a possessed underling makes an attempt on his life. By then, the aliens control the Midwest. The president orders Americans to strip to the waist, exposing the aliens, and at first this tactic seems to work. The aliens, however, control transmissions in the Red Zone and simply filter out the president's broadcast.
As aliens in Congress are uncovered and a military operation is authorized, Sam is sent to Missouri to learn if direct action will work against the threat. There he is appalled to find that almost the entire population is ridden by aliens. He fights his way out but doesn't make it back in time to stop the impending attack, and the military's expeditionary force, swamped by sheer numbers, is absorbed into the collective.
The overwhelming number of alien-infected humans makes the situation seem hopeless, and Sam and Mary--who have fallen in love--fear the worst. But the Old Man discovers the key to victory buried in Mary's mind, in the circumstances of a childhood trauma. A desperate solution is found, as dangerous as the aliens themselves, but they must take the terrible gamble if they are to save the human race.
An under-cover invasion
There are several intriguing aspects to The Puppet Masters. At one point, an alien takes possession of Sam, and for the next two chapters Heinlein gives readers both an innovative picture of what possession is like from the victim's viewpoint, and hints and glimpses of the alien's perspective. Afterward, Sam's trauma over this ordeal, and his terror of undergoing it again despite his training, is very real and adds dimension to his otherwise can-do agent character.
On the down side, the level of sexism in this novel seems extreme even for 1951. When present, women are considered, if at all, with either lust or disdain. It starts with Mary, whose main contribution for most of the story is sexual: If a man doesn't give her the eye, he's possessed. Later, when a character uses Mary to trick Sam into doing something he doesn't want to do, Sam tells himself he shouldn't feel betrayed by Mary--not because she's innocent, but because she's "just a babe." (Later, Sam, in the hospital, unburdens himself to a nurse named Doris--and it turns out she hates women as much as he does!)
Heinlein might have intended this anti-female bias as a comment on society, but normally when this is the case, sexism is a key plot element and affects the story's development. In The Puppet Masters, however, it's isolated from the story and affects it only as a taint. Usually a character who says "Most women are damn fools and children" has a good reason in the context of the story; these characters don't.
There are one or two plot holes as well: Particularly, a person is killed and later replaced by a duplicate, though this isn't within the aliens' capabilities. Nonetheless, The Puppet Masters does work as an adventure yarn about humanity rallying to preserve itself against an unusual and hard-to-fight enemy.
