During the 1870s Scotland, mining engineer James Starr receives a letter from his old colleague Simon Ford who is living with his family in a cottage deep inside the abandoned Aberfoyle mine.Ford asks for Starr's help to solve mysterious and unexplained occurrences taking place deep inside the Dochart well of the Aberfoyle mine.Starr and Ford explore the mine and they discover a new vein of coal.The discovery revitalizes the local mining community, which has been out of work since the mine's closure.The new mining project leads to the development of a vast underground mining town built around an underground lake called Loch Malcom.However, the mysterious occurrences continue to take place and they threaten to destroy the new found prosperity of the underground mining town.