Professor Alice Roberts is in Glasgow to investigate the impact of steam power on Britain's major towns in the 18th and 19th centuries. She also learns about the arrival of migrant workers in the city and how the insanitary conditions in which they lived, which made Glasgow both a hotbed of disease and a place of great medical advancement. Aerial archaeologist Ben Robinson flies his drone over Loch Katrine as he tells the story of how Victorian engineers overcame geographical barriers to bring fresh drinking water to the workers of Glasgow