Book excerpt: An officer at the Russian embassy—a man known as Calculus—has approached the FBI offering to sell a list of Americans who are giving confidential information to the Russian SVR. But before a deal can be made, Calculus is recalled to Moscow, and the Bureau fears the Russians will be hunting down and killing the traitors unless the FBI can find them first. FBI agent-turned-bricklayer Steve Vail thought he was done with the agency, but the Bureau has another unsolvable problem, and it has Vail's name written all over it. Finding the hidden turncoats, however, won't be easy—in fact, it could be downright deadly. And even with the help of FBI Assistant Director Kate Bannon, the Bricklayer's going to have to come up with a few new tricks of his own if he hopes to survive. Agent X: a white-knuckled thrill ride that crackles with an electric authenticity only a writer who's a real-life FBI veteran can provide.