Here's the BBC's synopsis of the programme: Eddie Butler travels to Merthyr Tydfil to explore its rich, and at times, surprising history. Once the largest producer of iron in the world, Merthyr is best known for the role it played in the Industrial Revolution. But Eddie discovers another side to Merthyr, full of radicalism and innovation. From the world's first steam locomotive, to Wales's first red flag of revolution, from the seeds of the Labour Party to the birthplace of Dr Joseph Parry. Eddie reveals the events and people that have shaped this Welsh valleys town.