London 1864. On a Hackney bound train, a guard discovers blood in a first class carriage - and a body on the railway embankment. For the first time, a murder has taken place on Britain's railways. Over a hundred years later, this single documentary for BBC Two uses the first hand testimony of the people involved at the time to explore this unique event and how it provoked a huge public outcry and debate. The story quickly became a news sensation as the dangers of the brave new world of the train were laid bare. Over a hundred years later, the witnesses to this story may be long dead but their words survive in court transcripts, memoirs, letters and vivid journalism. These testimonies are now used to tell the story, taking the documentary deep into the nineteenth century to meet an extraordinary cross section of real-life Victorian London - from the engine driver who found the body to the detective in charge of the investigation. Who killed Mr Briggs?