Set in the early 1990s, when Her Majesty's Customs and Excise was losing its battle with illegal drug smuggling (across Britain's borders), a group of British Customs employees are sent undercover to infiltrate some of the U.K.'s most dangerous criminal (drug) gangs. However, these were not trained spies; they were normal men and women, plucked from their ordinary lives, and placed into this top-secret operation. After going through a basic training regime, they were tasked with building new identities in the criminal underworld. These identities were called Legends.