Defector, The by Daniel Silva
Grigori Bulganov once saved Gabriel Allon's life in Moscow—and Allon always repays his debts. So when the former Russian intelligence officer vanishes, Allon gathers his team of operatives to go after those responsible. But, in a running battle that rages across the globe, Allon soon realizes that his enemy may already hold the key to victory. And that if he continues, it will cost him more than he can bear...
From the Paperback edition.