From Ovid's advice to use milk for illicit love notes to John Gerard's dramatic escape from the Tower of London aided by orange-juice ink messages—and al-Qaeda's hidden instructions in pornographic movies—Kristie Macrakis presents a history of invisible writing, uncovered through stories about scoundrels and heroes. A professor of history, technology, and society, as well as the author of Surviving the Swastika and Seduced by Secrets, Macrakis tells stories of adulteries unmasked, battles won, and history changed, charting the evolution of secret messaging and its impact on history.

"From parlor trick to weapon of war, invisible ink and other means of hidden writing emerge as one of mankind's more intriguing inventions in this lively history.... An engrossing study of unseen writing and the picaresque misadventures of those who employ it."—Kirkus Reviews