Wow you have read "a spy among friends " by Ben Macintyre an historian ,the best spy book ever in my view ,so intriguing and factual , he has also written other intriguing true stories "zig zag" "Double Cross"" .
Other recommendations:

Anything by Le Carre. (He worked for secret service)

Stumbled on another good spy writer Charles Cummings his "spy by nature" its first class (he was nearly recruited by the secret service,which adds to the intrigue ).

All have believable intriguing stories.