On Valentine’s Day 1929, seven men were gunned down in a Chicago garage in an attack that stunned the nation. Photographs of the bloody scene appeared on front pages across the country, and the public reacted with horror. Even in Chicago—a city hardened by daily gang violence—the message was clear: this was different. City officials were under intense pressure to respond, and suspicion quickly fell on the city’s most powerful gang leader, Al Capone. But proving who ordered the hit would be far more difficult than expected. And as investigators struggled to build their case, the fallout from the massacre would change Chicago—and Capone’s fate—forever.