Preposterous story, but no more than Line of Duty, which also stars Martin Compson. In fact he appears to be playing the same character, but he's off duty in this. Loads of plot holes and strange decisions by the characters but it's fiction not real life. The constant use of flashbacks can be a bit confusing at times, but overall I found it quite entertaining and the final episode contained a few surprises and came to a reasonable conclusion.
