Parasitical aliens attach themselves to human hosts and take over their bodies. Two spies are sent to find out what's happening, but the extent is much farther than they knew. With access to the humans' memories, the aliens quietly invade the government and start taking over.
Source · ISFDB CC BY 4.0
Placement
- contained in A Heinlein Trioomnibus
- contained in Robert A. Heinlein: Beyond Time and Space with the Master of Science Fictionomnibus
- contained in Three by Heinleinomnibus