How did German intelligence agents use a dead fish to convey critical information to their operatives? What did an advertisement for a dog in the Times have to do with the movement of British troops into Egypt? And why did British officers suddenly become suspicious of the trousers hanging on a Belgian woman’s washing line?

Throughout World War I, spymasters and their networks of secret agents developed many clever—and sometimes comical—methods of covert communication. Stacks of bread in a bakery window, puffs of smoke from a chimney, and even woolen pullovers were all used to pass on secret messages that were decipherable only to the well-trained eye. Drawing on the memoirs of eight spies, Melanie King divulges these and other tricks of the trade while sharing details from their astonishing stories. Among her informants are British intelligence officers working undercover in Germany and France, including a former Metropolitan police officer who once hunted Jack the Ripper; a German secret service officer codenamed “Agricola;” an American newspaperman; and an Austrian agent who disguised himself during his career as everything from a Jewish peddler to a Russian officer.

A fascinating compendium of clever and long-forgotten ruses—interspersed with the stories of the spies themselves—Secrets in a Dead Fish sheds new light on the shadowy world of Great War espionage.