In Pontypridd and the Rhondda in 1905, coal is king and the families who sunk the first collieries are rich. None is wealthier or more generous a benefactor than Harry Watkin Jones. His daughter Sali is about to marry her childhood sweetheart, but tragedy follows tragedy, and four years later Sali is a penniless outcast, fleeing from a violent husband and struggling to support herself and her son in a difficult world. Sali finds work in the home of family of colliers, and here she and her son find the warmth and love missing from their lives for so long. But unrest and violence have come to the valleys. Caught up in the conflict, Sali finds herself denying her roots, her class, and even sacrificing her son's future, for the sake of the people she loves and the cause they are prepared to die for.