The Talbot Odyssey by Nelson DeMille

IT STARTED AS A SIMPLE SPY HUNT.
IT BECAME A DESPERATE BATTLE TO SAVE THE WEST.

For forty years Western intelligence agents have known a terrible secret: the Russians have a mole -- code-named Talbot -- inside the CIA. At first Talbot is suspected of killing European agents.

Then a street-smart ex-cop uncovers a storm of espionage and murder on the streets of New York, while in a Long Island suburb a civic demonstration against the Russian mission masks a desperate duel of nerves and wits.