My Adventures as a Spy — Robert Baden-Powell

It has been difficult to write in peace-time on the delicate subject of spies and spying, but now that the war is in progress and the methods of those much abused gentry have been disclosed, there is no harm in going more fully into the question, and to relate some of my own personal experiences. Spies are like ghosts -- people seem to have had a general feeling that there might be such things, but they did not at the same time believe in them -- because they never saw them, and seldom met anyone who had had first-hand experience of them. But as regards the spies, I can speak with personal knowledge in saying that they do exist, and in very large numbers, not only in England, but in every part of Europe. As in the case of ghosts, any phenomenon which people don't understand, from a sudden crash on a quiet day to a midnight creak of a cupboard, has an affect of alarm upon nervous minds. So also a spy is spoken of with undue alarm and abhorrence, because he is somewhat of a bogey.