On an August afternoon in 1910, a Polish nationalist gunned down an alleged Russian spy on the streets of Kraków. Afterward the murderer claimed that he had done a great deed for “Poland,” though no such country existed at the time. The press lionized the assassin, justifying his act as necessary for the defense of the nation. When the defendant stood trial, a jury composed of local citizens acquitted him, and he walked free.How does an ordinary, working-class man transform into a political executioner? And how does a society reach the tipping point where premeditated murder is celebrated as a civic duty?This gripping historical investigation unravels the environment and conditions of radicalization in fin-de-siècle Europe. Societal shifts, mass political movements, the popular press and espionage paranoia all contributed to a fearful community, wary of outsiders and ready to do anything to defend itself.