1860s Swansea, where copper can make your fortune – at a price. John runs away to sea to escape rural poverty. The ocean fuels his wanderlust and he becomes a master mariner. Margaret, a fiery Gower farmer’s daughter, falls in love with his adventurous spirit. A pioneering woman of her era, she learns to navigate, and they sail together, sharing a passion for the ocean. When John’s ship is wrecked, rumours that it was scuttled jeopardise his reputation. Short of options, John gambles on the copper trade with Chile, skippering a ship round Cape Horn – the ultimate test of seamanship but a graveyard for crews. Meanwhile, Margaret uncovers the damage copper inflicts on Swansea’s community, causing destitution and deadly pollution, as smelter Vernon grows rich. Horrified, she collaborates with shipowners conspiring to wrest control from Vernon. But when Vernon discovers the plot, the family’s reputation and livelihood is at stake…