The other woman / Daniel Silva.

Enhanced descriptions from Syndetics:

From Daniel Silva, the #1 New York Times -bestselling author, comes a modern masterpiece of espionage, love, and betrayal.

She was his best-kept secret ...

In an isolated village in the mountains of Andalusia, a mysterious Frenchwoman begins work on a dangerous memoir. It is the story of a man she once loved in the Beirut of old, and a child taken from her in treason's name. The woman is the keeper of the Kremlin's most closely guarded secret. Long ago, the KGB inserted a mole into the heart of the West--a mole who stands on the doorstep of ultimate power.

Only one man can unravel the conspiracy: Gabriel Allon, the legendary art restorer and assassin who serves as the chief of Israel's vaunted secret intelligence service. Gabriel has battled the dark forces of the new Russia before, at great personal cost. Now he and the Russians will engage in a final epic showdown, with the fate of the postwar global order hanging in the balance.

Gabriel is lured into the hunt for the traitor after his most important asset inside Russian intelligence is brutally assassinated while trying to defect in Vienna. His quest for the truth will lead him backward in time, to the twentieth century's greatest act of treason, and, finally, to a spellbinding climax along the banks of the Potomac River outside Washington that will leave readers breathless.

Fast as a bullet, hauntingly beautiful, and filled with stunning double-crosses and twists of plot, The Other Woman is a tour de force that proves once again that "of all those writing spy novels today, Daniel Silva is quite simply the best" ( Kansas City Star ).