Round about the second anniversary of the start of World War 1, Roger Waterlow is still stuck ashore in charge of the ramshackle British naval intelligence effort in a sweltering notionally ‘neutral’ country in South-eastern Europe. As rumour follows rumour and the situation becomes daily more confused, Waterlow and his organisation learn of three couriers trying to carry correspondence to Berlin—correspondence that might give the Entente powers vital insights into German intentions for the region, if only they can be intercepted and their papers seized…