What drives some people to take the law into their own hands? Mike Williams hears stories from Europe, Africa and the US. Stories about the men – and it is usually men – who take it upon themselves to patrol the streets or seek out paedophiles online. And, he explores what happens when vigilante groups mutate into monsters. Whether motivated by revenge, frustration or a desire to do good, does mob justice ever work?

With contributions from Scott and Callum, co-founders, Dark Justice; Laurie James, forensic criminologist, based in Botswana; Curtis Sliwa, founder of Guardian Angels; Kate Meagher, associate professor, Department of International Development, London School of Economics; Jim Gamble, former chief executive, Child Exploitation and Online Protection Centre; Abubakar Bukar Kagu, solicitor and advocate of the Supreme Court of Nigeria

Photo: Close up of Guardian Angels' jacket with other men sitting in background, Credit: Mario Tama/Getty Images