Centuries ago in middle Europe, a coded language named Rotwelsch appeared, scrawled in graffiti and spoken only by travelers, Jews, and thieves. This flexible argot unsettled those in power, who responded by trying to stamp it out, none more vehemently than the Nazis. As a boy, Martin Puchner learned Rotwelsch from his family, but later discovered that his own grandfather had been a committed Nazi who hated everything it stood for. Interweaving family memoir with a foray into linguistic mysteries, Puchner recounts how—in a language born of migration and survival—he discovers a witty and resourceful spirit of tolerance that remains essential in our volatile present.