An invasion of Earth via means of 'slugs' which attach themselves to people and control their actions. The story is told from the viewpoint of an elite government agent looking back on the situation as it was discovered.Lacking the sensawunda of his juveniles, or any particularly interesting speculative idea, this is a fairly rote alien invasion. There is some frustration at the idiocy on display at times - they recover alive a person with a slug attached, detach the slug, then have a big moral debate about putting the slug back on him so they can interrogate the slug. This stupidity is then followed by scenes of difficulty convincing people in charge that the slugs are real. Sigh.The story follows a fairly common route for alien invasion stories - the population is near overwhelmed, then find a way to fight back. It had its entertaining aspects, but isn't really that memorable.Like most of Heinlein's books, it's difficult to be female and focus on the story. It's full of statements like: "Listen son, most women are damn fools and children" and "Forgive me darling. I'm weak and womanish". Even compared to other books written in the 40s, it's bad.The story does open with a team featuring a competent male and female agent, but at the close of the story the female has been reduced to saying little but "Yes, dear" in blissful wifely servitude.