In August 1963, a Glasgow-to-London Travelling Post Office train was stopped in the English countryside by a false red signal. The gang that followed stole around 2.6 million pounds in banknotes, but the legend of the Great Train Robbery often hides the violence done to driver Jack Mills, second man David Whitby, and the postal workers on duty. This episode follows the false signal, the High Value Package carriage, Bridego Bridge, Leatherslade Farm, the Monopoly-board evidence, the huge investigation, and the way a celebrated heist exposed a national system's quiet security failures.