The introduction of steam railways in the early 19th century changed Britain in a way no one could have predicted. This episode explores how they created a domestic revolution, changing the way we lived, from the houses we lived in to the food we ate. In the middle of winter, the team arrive in Snowdonia to find out how millions of tons of slate were moved down the mountain. This is the slate that covers roofs in every corner of the country, and all of it was moved by rail.