The final film in the trilogy does tie things up satisfactorily, but requires so much leaping back and forth, I kept expecting a blue police-box to materialize. It centers on two figures, cop Maurice Jobson (Morrissey) and solicitor John Piggott (Addy), both of whom are seeking redemption of some kind - the former for his ongoing role in the corruption and criminal activity of the previous decade, the latter trying to restore his family reputation, destroyed by his father, who was a notoriously corrupt policeman. They form an unwitting team, after the abduction of another child, returning to the pattern of part one. This does expose the dubious conviction of a mental defective for the crimes depicted there, but the police simply find another scapegoat, a friend of the original "perpetrator." However, working the case from opposite ends, Jobson and Piggott gradually reveal the truth, and find out the true criminal.
Which, to be honest, is a bit of a disappointment. I don't want to give too much away, but after the first couple of movies, I was expecting something wide-ranging and conspiratorial. It's not really anything like that, and it means the series ends more with a whimper than a bang. I did like Piggott, who is about as far from the typical "hero" in these things as you can imagine. He's unwilling to get involved, and has any number of unpleasant personal habits - yet, he has a strong sense of right and wrong, which drive him even when it would be easier to quit. It's one of those films where the characters deserve a much better script than they get; here, the story even drags in a psychic, which is rarely more than a lazy device to allow the easy discovery of information necessary to the plot. By the end, while it has tied up most of the loose ends, others are ignored or disposed of in a confusing manner [we're still trying to work out who the body in the shed was at the end]. Overall, the series is a frustrating exercise: I can see the aim, and it occasionally works brilliantly, but it's a very qualified success.