The drama filmed in west Wales and south Wales for S4C.

The six-part crime drama is named after the river near the series’ main setting of Pembroke Dock and is penned by Welsh writer Catherine Tregenna, who is best known for her work on Three Pines, Lewis, DCI Banks and The Bench.

Tregenna said at the start of shooting: “I’m so excited to create and write my own series and share it with S4C audiences as that’s where my television career began. It’s a privilege to write in the voice and accents that are part of my childhood and bring to bear what I’ve learnt in over 25 years of writing crime thrillers.”

The Mallorca Files actor Elen Rhys stars in the drama – her first major role in Welsh, her mother tongue. Rhys plays DI Ffion Lloyd, who partners up with her ex-boyfriend DS Rick Walters (Richard Harrington) to find the killer of a nurse in a Welsh coastal town.

Sion Ifan is the director of all six episodes; the series is produced by Blacklight and supported by Creative Wales. Banijay Rights handles distribution for an English-language version – The One That Got Away – for international audiences.