DCI Tom Mathias (Richard Harrington, Poldark) is a brilliant, brooding loner who leaves London for coastal Wales, an isolated land of mountainous terrain and close-knit villages. DI Mared Rhys (Mali Harries) is a local who knows Aberystwyth inside out. Together they confront mystifying murders that will push Mathias to the edge in a place with secrets as dark and destructive as his own.