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.

Sharon Roberts has never stopped grieving the loss of her daughter, Ela. Joe Pritchard, a quiet, unassuming gardener, was arrested for Ela's murder after her DNA was found at his caravan. Joe confessed to killing Ela but wouldn't, or couldn't, say why or what he did with her body.

Journalist Cat Donato, originally from the same town as Ela, has always been obsessed by her murder. Ela had been part of her circle of friends but prior to her murder Ela had been ostracised over a silly teenage squabble, a fact that Cat has tried her best to forget. The news of Joe's parole hearing and the prospect of his release causes both women to confront the past and the part they played in Ela's final days.

With so many questions unanswered, Joe's return to the community could be a way to get to the bottom of the mystery once and for all. If Joe Pritchard did kill Ela, why did he do it, and where is the body?