After five years' silence, a British intelligence asset has made contact from Moscow. Claiming to possess explosive information, he wishes to defect to the West. But the operation goes catastrophically wrong; the would-be defector betrayed by a rogue element at the highest level of US government. As a result, MI6's Margo Lane is ordered to deliver a message the White House won't forget. Margo's mission will take her to the violent heart of contemporary Russia, the edge of the civil war in Syria - and to a terrifying decision she had hoped she would never have to make.