The series tells the story of detective DI Cadi John who returns to north Wales to care for her ailing father. However, when the body of a young woman is found in a local river, Cadi's world - and the world around her - is changed forever.

The bilingual version of the series, under the English name Hidden, was broadcast on BBC One Wales and BBC Four in 2018 and 2020.  The English-language version of the third and final series aired in April 2022.