BBC Scotland investigates the multi-million pound world of the legal high trade. Reporter Sam Poling tracks the supply chain of Britain's newest designer drugs, from their manufacture overseas to the devastation caused on the streets in the UK. Using secret filming, she exposes how those getting rich from this ruthless trade are evading the law. She meets the vigilantes who are confronting the legal high dealers head on with orders of exile, kneecappings and even killings. And she questions the UK government's ability to deal with the growing problem.