Black Ops by Stephen Leather
As an MI5 agent, Spider is used to going undercover, but when he is asked to assume the identity of the contract killer hired to take out President Vladimir Putin, he knows that he will become a wanted man. And things are about to become more complicated. Spider is told that his MI5 controller and close friend Charlotte Button has been running an off-the-books assas-sination operation, taking vengeance on the men who killed her husband. Spider owes his life to Button – but this discovery will stretch his loyalty to the limit….