The Head of British Intelligence is having a bad day. Only six months off retirement and Sir William Rentoul is wondering if he'll make it that far, what with the sudden descent of a brain fog dense enough to turn every day into a series of small humiliations.

To make matters worse, Parliament's Intelligence and Security Committee - the body that oversees Sir William - has received an anonymous complaint from one of his officers. Sir William dimly recalls accepting that there should be a channel for whistleblowers, but he never expected that they would pick his most sensitive case, one involving an Iranian assassin and a trail of dead bodies, or that the person who turned up to poke their nose into his files should be a lowly parliamentary researcher named Aphra McQueen, who displays smarts, tenacity and rebelliousness in unsettling measures.

Aphra seems to know more about the operation than she is letting on. What will she uncover? What is she really up to? And can she survive the unexpected events that will bounce her from London to Birmingham to Paris to Lausanne?