Y Golau: Dŵr returns to Llanemlyn, where a controversial redevelopment plan to expand the reservoir is reigniting old tensions. The story captivates Caryl, a young journalist, who becomes entangled in a complex web of personal betrayal, familial secrets, and dark mysteries, which raises doubts about the imprisonment of Rhys Owen for the murder of his cousin Llŷr during the protest against the expansion in 1995.