The Black Indies (1964)

In 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 Starr to help solve mysterious unexplained happenings taking place deep inside the Dorchat well of the Aberfoyle mine. Starr and Ford explore the mine and discover a new vein of coal, which 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, Loch Malcom. However, the mysterious occurrences continue, which threatens to destroy the newfound prosperity of the underground mining town.