The Increment by David Ignatius: A Novel Paperback

Harry Pappas, chief of the CIA's Persia House, receives an encrypted message from a scientist in Tehran. But soon the source of secrets from the Iranian bomb program dries up: the scientist panics; he's being followed, but he doesn't know who's on to him, and neither does Harry. To get his agent out, Harry turns to a secret British spy team known as "The Increment," whose operatives carry the modern version of the double-O "license to kill." But the real story is infinitely more complicated than Harry understands, and to get to the bottom of it he must betray his own country.