Henry Landau was a young South African serving with the British Army when he was recruited into the British secret service, the organisation we now know as MI6, which needed a Dutch speaker to run its agent networks in Belgium. Talent-spotted by one of the secret service's secretaries on a dinner date, Landau was summoned to the service's headquarters in Whitehall Court to meet Mansfield Cumming, the legendary 'Chief' of the service and the original 'C'. Cumming, who had a wooden leg and tested the character of his young recruits by plunging a paper knife into it, sent Landau to Rotterdam, from where all the British spy networks in Belgium, France and Germany itself were run. Landau's main task was to run La Dame Blanche, a group of more than a thousand Belgian and French agents who monitored the movement of German troop trains to and from the Western Front. Named after a mythical White Lady whose appearance was supposed to presage the downfall of the Hohenzollerns, it was arguably the most effective intelligence operation of the First World War and, according to Cumming, produced 70 per cent of all Allied intelligence on the German forces.