Binged this today. It was OK but nothing special. The casting was fine and the story engaging but the 1st two episodes are more or less unrelated to the last two. I know the UK is the King of the mini-series but give me a break. A series with only 4 episodes doesn't need to be subdivided any further. If each half were aired across two seasons then fine...kinda like Prime Suspect but that it not the case here. Maybe the goal was for this show to last longer with multiple "who done it" arcs but was cancelled early on but with sunk costs to consider the creators were told to produce it as a 4 part limited mini-series and so they stitched two arcs together and called it a day. I wouldn't pay to rent/buy this individually but it is a perfectly fine watch if available to you through a free or already subscribed to streaming service. There are plenty of better BBC produced copper shows out there though.
Review of In the Dark
