Interesting spin on the usual police investigation story, that starts with the incident and then unravels the story over the 5 episodes as the main characters piece together what happened. Douglas Henshall is excellent as usual, in his trademark moody Scottish leadership role (see 'Shetland' for more Henshall) and the background story move along reasonably well. This had so much potential, with the calibre of the acting and the plot, it could have easily have been renewed for more than one outing, if only the producers had the foresight to take the format forward. The basic premise of the show, that of a road traffic accident and the subsequent investigation of all the many variables that led up to the crash, offers the possibility of many different season arcs as the characters investigate different scenarios over a number of episodes. If this had been an American show, I'm sure it would have been renewed.
Nice twist at the end, which adds a whole new dimension to the whole story :)