"I've been a scoundrel, a thief, a blackmailer and a whore, but never a murderer. Until now..." The year is 1929. As the world teeters on the brink of a global recession, Bletchley Park plays host to a rather special event. MI5 is celebrating its twentieth anniversary and a select band of former and current employees are gathering at the private estate for a weekend of music, dance and heavy drinking. Among them is Sir Hilary Manningham-Butler, a middle aged woman whose entire adult life has been spent masquerading as a man. She doesn't know why she has been invited - it is many years since...

"Your predecessor was sitting in that chair when he shot himself. You can still see the blood stains on the wall behind you." Central America, 1931. Hilary Manningham-Butler is settling into her new job as passport control officer at the British legation in Guatemala City. Her predecessor Giles Markham is dead, having embezzled a large sum of money from the office's visa receipts and then taken his own life. Freddie Reeves, a friend at the legation, believes there is more to his death than suicide. The weekend before he died, Markham spent some time at a remote coffee plantation in the north...