Lovely Katie Cullen is all alone in the world. Her mam has died, and Swansea is now no fit place for a young girl on her own. The navvies who are building the new railway roam the streets on pay day looking for trouble, and the peaceful outskirts are transformed into a shanty town as the silver track wends its way to the town centre. So when Katie meets handsome Bull Beynon, the foreman of the railway builders, she falls in love with him at once and longs to be protected by him. But Bull has his own woman, the spirited Rhiannon who lives with him in their simple shack by the side of the railway track. Katie and Rhiannon find that they are caught in a network of lies and deceit as their lives become interwined with those of the women at the Mainwaring Pottery. Secrets and love affairs bring tragedy in their wake in the town now dominated by the monster they call the Great Western Railway.