CHAPTER ONE   Monday, 0900   It might come as a disappointment to learn that the natural habitat of the intelligence officer is not the shooting range or the gym mat, the departure lounge of a hot and dusty airport, the safe house or the interrogation cell. It’s not halfway up a ladder aimed at the draughty rear window of a foreign embassy. It’s not even the street, the simple street – narrow, damply cobbled, thick with London fog and Russian menace. No, the natural habitat of the intelligence officer is the meeting room. Spies like to talk. “You will have heard of a section called Gatekeeping,” says Charles Remnant. “In simple terms, we investigate the insider threat – the threat posed by our own members of staff, who may have been recruited by hostile foreign powers. What you will not have heard of, however, unless matters have really got out of hand, is the secret cadre of officers we refer to as Gatekeepers.” In this case, not just any meeting room, but one at the top of the building, one at the dead end of a corridor otherwise used to store broken filing cabinets and unused safes. The paint…