The scandalous 1866 publication of 'A Night in a Workhouse' altered the course of press history. Victorian journalist James Greenwood's disconcerting exposé of spending a night in a casual ward while disguised as a vagrant launched an enormously popular genre of newspaper writing that would come to be known as undercover reporting. Inspired by the exploits of the 'Amateur Casual', imitators infiltrated restricted areas by adopting disguises of their own as beggars, migrants, homeless people, mental patients, street performers, and single mothers. Undercover traces the seismic consequences that the radical innovation of 'going undercover' had for Victorian media, literature, and culture. This revisionist history of a distinctly British tradition of investigative journalism reconstitutes the pioneering investigations that shaped the global development of undercover reporting, analyses the format's vicarious appeal to audiences anxious about their own precarity, and traces the impact that incognito investigations had on the Victorian era's leading novelists.