In 2007 the government tasked Britain's 55 police forces to tackle the trafficking of women into the country for sex. This first programme documents the initial stage of the operation, in which the police raid brothels across the UK and use victims' testimonies to garner intelligence about the criminal networks that run them. The film follows Detective Constable Andy Leigh as he gathers evidence through covert filming, information from local estate agents and liaison with other forces to build a picture of what's happening across the nation. All brothels under surveillance are raided at the same time to maximise the amount of evidence from victims, customers and the brothel managers. What emerges is a tale of innocent women, brought and sold into sexual slavery. The evidence enables the police to take their first steps up the ladder from the brothel managers to the criminal masterminds responsible for the illicit trade.

The second programme in the series follows the police as they close in on nationwide criminal gangs. Many of the women rescued from the brothels are too frightened to talk. But, in Devon, one woman, 'Lily', has been brave enough to come forward and tell the police of a massive trafficking network that stretches round the world. Detective Sergeant Ian Tomlinson explains how Lily had unwittingly been trafficked from Thailand, ostensibly to work in the Irish restaurant trade. Instead, she was sold to a London brothel, where she was terrorised and blackmailed into becoming a prostitute. Her testimony enables the police to close in on the elusive people responsible for bringing girls into the country. And, as the police net begins to close, the criminal masterminds are flushed out of hiding, revealing the next link in the chain that connects slave markets in Britain with criminals on the other side of the world.

In this final film, the police target slave markets in Britain, where women are traded, and close in on the international masterminds at the head of this global, multi-million-pound industry. One of the few victims to come forward, 'Lily' has provided valuable leads, resulting in the arrest of her trafficker, the brothel managers, the man who 'ordered' her from Thailand and the organisation's banker. Now the police are on the trail of the woman who bought Lily for £30,000, who they suspect is buying women from auction houses and slave markets around the country. As the police hunt for a slave market in central London, knowledge of the trafficking operation widens. The network takes them thousands of miles from their regular beat, to Bangkok, where police in Thailand are also breaking up criminal gangs. And, after months of intense investigation, the police operation finally secures convictions, and gives the police and victims a chance to reflect on their experiences.