"The Puppet Masters" is a science fiction novel written by Robert A. Heinlein, published in 1951. The story follows a group of humans who encounter alien parasites that attach themselves to their hosts, controlling their actions. The narrative explores themes of free will, manipulation, and the struggle against an unseen enemy. The plot centers on a government agent, Sam C. McGowan, who works to uncover the truth behind the alien invasion. As the parasites spread, he and his team must find a way to combat the threat while grappling with the implications of losing their autonomy.