The 'Ndrangheta operates out of Calabria, in Italy's toe, and has grown into one of the country's most powerful crime syndicates while staying largely out of the headlines that follow the Sicilian Cosa Nostra or the Neapolitan Camorra. This film tracks its business: drug trafficking, extortion, and money laundering operations that investigators estimate account for at least 3% of Italy's GDP. It traces the organization's roots to the 1950s, when it began expanding from rural Calabria north through Italy and eventually into international networks. Law enforcement officials and organized-crime experts appear on camera describing how the group's family-based structure and strict codes of silence have made it far harder to infiltrate than its better-known rivals, and footage from undercover operations shows some of the methods used to try. The bunkers of the title are literal: hidden structures built to shelter fugitive bosses and stash operations from raids, part of a broader picture of an organization built to survive direct assault by staying invisible.