In the early 1990s, Her Majesty’s Customs and Excise was losing its battle with illegal drug smuggling across Britain’s borders. The solution was extraordinary. In a top-secret operation, a small team of Customs employees were sent undercover. Their task - to infiltrate Britain’s most dangerous drug gangs. But these were not trained spies. They were normal men and women, plucked from ordinary lives around the UK, put through a basic training regime and tasked with building new identities in the criminal underworld. These identities were called Legends.