It’s early December 2014, and at the Hyatt Regency hotel in Rosemont, Illinois, an unusual gathering is taking place. It’s the final night of Midwest Furfest, the world’s largest convention for a subculture known as Furries.The party is in full swing when, just after midnight, attendees suddenly find themselves struggling to breathe. Something terrible has happened: poisonous levels of chlorine gas are sweeping through the hotel corridors.Nineteen people are hospitalized and hundreds are evacuated into the freezing cold, many still wearing their colorful anthropomorphic animal costumes, or fursuits. Hazmat teams trace the gas to a stairwell, where...