In 1855, New York City was scandalized by one of the most infamous murders in its history, that of gang leader Bill "the Butcher" Poole, the feared knife-fighter who later would inspire Daniel Day-Lewis's character in Martin Scorsese's film The Gangs of New York. The acknowledged mastermind in the Butcher's undoing was John Morrissey, a two-fisted Irish immigrant who, more than any other man of the age, represented the nefarious links between organized...