Intelligence officers working under diplomatic protection are rarely out of the news for long, and the last two years have been no exception. Strong circumstantial evidence has accumulated that they have played some role in cultivating even the President of the United States as an agent of influence for Russia. How did the relationship between diplomacy and secret intelligence come about? What was the impact on it of the bureaucratization of secret intelligence that began in the late nineteenth century? Is diplomatic immunity the only reason why intelligence officers still cluster in embassies and consulates today? What do their diplomatic landlords think about their secret tenants and how do the spooks repay the ambassadors for their lodgings? These are among the key questions considered in this historically grounded work on the contemporary interface between diplomacy and secret service. It also has guidance on further reading and contains numerous illustrations.