Spring, 1858. The route of the Caledonian Railway through the Scottish countryside is disrupted by a fatal crash. The Railway Detective Inspector Robert Colbeck and his trusty Sergeant Victor Leeming are called from London to investigate, and must contend with old enemy Superintendent Rory McTurk to uncover the criminals behind the disaster. The motive for the crash is unclear, with suspects including the North British Railway, a group of sabbatarians and those with personal vendettas to pursue. Can Colbeck and Leeming crack the case before the Royal family makes their train journey to Balmoral?