How did German intelligence agents in the First World War use dead fish to pass on vital 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 personnel become suspicious about the trousers hanging on a Belgian woman’s washing line?

During the First World War, spymasters and their networks of secret agents developed many ingenious – and occasionally hilarious – methods of communication. Puffs of smoke from a chimney, stacks of bread in a bakery window, even knitted woollen jumpers were all used to convey secret messages decipherable only by well-trained eyes.

Melanie King retells the astonishing story of these and many other tricks of the espionage trade, now long forgotten, through the memoirs of eight spies. Among them are British intelligence officers working undercover in France and Germany, including a former officer from the Metropolitan Police who once hunted Jack the Ripper. There is also the German Secret Service officer, codenamed Agricola, who spied on the Eastern Front, an American newspaperman and an Austrian agent who disguised himself as everything from a Jewish pedlar to a Russian officer.

Drawing on the words of many of the spies themselves, Secrets in a Dead Fish is a fascinating compendium of clever and original ruses that casts new light into the murky world of espionage during the First World War.