In 1962 the young Patrick Marnham set off by car for a small village in central France. There he was taught French by an imperious countess, who he later discovered had fought in the Resistance until, betrayed, she was sent to Ravensbrück concentration camp. On the very same day that his hostess's network was broken, Jean Moulin, de Gaulle's delegate as head of the combined Resistance forces, was arrested in Lyons, where he was tortured by Klaus Barbie before dying in Gestapo custody. Was this coincidence, or were these events connected? The anonymous letter writer suggested a key to the mystery.

Using a knowledge of France gained from 12 years as the Independent's Paris correspondent, and subsequent research in archives in England and France, Marnham set out to discover the truth about the betrayal of the old lady who had become his tutor and friend. Following a trail leading from London through Occupied Europe to the rank and file Resistance in lost corners...