I'd highly recommend all of his books.
Bamford has quite extraordinary access to the NSA - and many contacts outside to balance what Fort Meade tells him.
Collectively, his writings chart the classified history of signals intelligence from the signing of UKUSA through to the Snowden era.
It's like reading a parallel history of international geopolitics from 1949 onwards - fascinating.
And as the Internet has grown, so have Five Eyes SIGINT partners wrapped themselves around it and inveigled their way into its furthest reaches, like a vine, as Snowden revealed.