Posted by Tintin (here)
John Hughes Wilson's book: "The Puppet Masters" does delve back a lot further into the history of intelligence - a particularly interesting piece in that book covers Crassus (I think 2nd or 3rd century Roman) and his 'fire brigades'.
JHW has mentored my brother who's in the UK military, in intelligence, and also went to school with my father although I am not certain that they were properly acquainted but in the same year.
He's an interesting character himself.
I've just ordered a used copy of the puppet masters book from amazon. Reading it will be a chore though. I much prefer a few audio interviews with the authors of books than actually reading them. My natural inclination is to skim and amalgamate broadly.