The Puppet Masters is a 1951 science fiction novel by American writer Robert A. Heinlein, in which American secret agents battle parasitic invaders from outer space. It was originally serialized in Galaxy Science Fiction (September, October, November 1951). The book takes up the then common theme of sightings of Flying saucers, the plot assuming that the "saucers" seen in the 1950s were part of a preliminary reconnaissance of Earth, carried out by the extraterrestrials in preparation for a full-fledged invasion sixty years later.