"Mole-hunt: The Secret Search for Traitor That Shattered the CIA", authored by: David Wise.
This book brought me a stunning secondary perspective. Upon reading "The Ghost: James Jesus Angleton" as well as "A Spy Among Friends", I was under the impression that James Jesus Angleton was most adamant about penetrating the CIA for Soviet moles, upon after having the revelation bestowed to him, that his closest friend (Kim Philby) was a high-ranking Soviet defector.
David Wise presents evidence that expresses otherwise. He states that upon Anatoly Golitsin (KGB defector) debriefing being monitored by James Jesus Angleton, and Angleton hearing him tell the CIA interrogators: "The mole was someone of Slavic background whose name might have ended in sky. He had been stationed in Germany. His KGB code name was Sasha, and, the true last name began with the letter K", that Angleton began his frenzied penetration of the CIA in hopes of finding the mole.