On the surface this three series crime drama appears to be a Welsh 'Midsomer Murders' but a lot darker. The brooding landscapes, the subdued photography and lingering stares between the main protagonists all adding ingredients to the atmosphere.
However, the first few episodes hint at an underlying story which gradually becomes apparent and is not fully resolved until the final episode of the last series.
In the mean time there are episodes of totally unrelated, 'stand alone' murders, mixed in with incidents connected with the ongoing theme.
Once you have watched all three series you will want to start again from the beginning to pick up on all the threads you may have missed in hindsight of the finale.