This documentary tells the inside story of one of the National Crime Agency's largest money laundering investigations. With unique access to NCA documents and surveillance footage, the programme traces an extraordinary nine-month operation, which started with undercover surveillance on one man, and ended up with over 100 officers bringing down one of the largest criminal networks in the country, worth over £180 million. Every year, more than £100 billion changes hands in Britain illegally. Much of the money is controlled by international criminal networks that are involved in drug smuggling, human trafficking and even terrorism. Many British drug dealers outsource the cleaning of their dirty cash to specialist money laundering groups, who collect the money by hand and ensure it's paid out to the right person in the right place, anywhere in the world. These groups operate with a strict hierarchy and a sprawling network of agents, each with different roles.