The Puppet Masters, by Robert Heinlein

When I came across this sci-fi classic at the library, I couldn't resist reading it.  First published in 1951, it is a touch dated and certainly has a male chauvinist tone.   But these issues don't really get in the way of an enjoyable story.  Mr. Heinlein's later works are much more my favorites, but his stories are consistently interesting.

The Puppet Masters