Good until the last episode then the plot collapsed, didn't it?
Don't read any of this if you've not seen the last episode, obviously.
The reveal indicates that Denton is not involved in any long standing part of the corrupt police element. Her involvement starts when was following her (ex?)-boyfriend and caught him out with the 15 year old girl. At that stage she doesn't know anything about a plot involving organised crime,witness protection, and her ex.
Why does she avoid the CCTV? She has managed to avoid the CCTV in the car park (cleverly and deliberately argue AC12 in the investigation) without having any knowledge that in the future she would want to avoid being seen on CCTV (and therefore, incidentally, would have had no reason to know whether or not she'd been captured on CCTV and would be safe to deny her presence later to AC12). As far as she knows or has any reason to believe the only person who may be interested in her presence or not at the scene is her ex bf who sees her anyway and she is not trying desperately hard to hide from.
Why not help the girlShe then sees two males make an attempt to kidnap the girl and in the process assault her. There is still no particular reason for her to suspect a sophisticated blackmail plot, no cameras seen or anything, it would much more likely be put down to an irate pimp who is upset she hasn't made any money. Fair enough, two males against her, she may not want to take them on, but she is an exemplary officer who surely would either call for backup and intervene in the assault and attempted kidnapping.
Why investigate secretly? She then investigates the driver of the motor vehicle etc, again at this point there is no reason to suspect anything like the blackmail plot. If she was concerned, her ex already knows she is there, why not tell him about it. Why keep her investigations secret?
Why use the sergeant's computer to check the records? There seems no reason to make her investigation secret, but even if she does wish to, a detective must habitually check motoring records of suspects, and indeed from personal experience I know a PC can call up for records very easily. She has no reason to think that any complex murder plot will incriminate her so she has to avoid being seen to investigate the case - she still doesn't know who the male is who is involved. Indeed if she wanted to keep it secret using the sergeants computer would surely raise suspicions of her actions even if he is unlikely to specifically complain about it because of his minor improper use of the computer.
Why enter into the conspiracy? If she wanted to nail Tommy why not investigate for blackmail or for kidnapping, sexual exploitation, or indeed for murder if she found out the girl was missing? Immunity from prosecution does not cover future offending and he would be open to prosecution for any of those crimes.
How does she know the tracker is on her car? It could equally be on Ackers, or in the car rather than on the car, but she finds it quickly at night having just been involved in an accident.
why don't the criminals try to kill her? They have no compunction about killing the PCs guarding Tommy. They have set her up with cash and contacts with Ackers to show she is involved in the conspiracy. If they kill her then it would be case closed, finding the money and investigating her the police would think the only corruption would be linked to her and Ackers and no further in depth investigation would follow.
Why do the criminals try to kill her having decided not to kill her, the assassins are then instructed to kidnap, torture, and murder her anyway. And in any event...
How do the assassins know she is going to be transported along that road to kidnap her at that particular point? Not only do they do so in broad day light but commandeer a car (therefore showing themselves to civilians)
How/why are prison staff involved in threatening Denton? They say they don't want her talking to AC12, but the only thing she could tell AC12 is the extent to which Ackers involved her in a plot to kill the witness, thereby confessing to her involvement in the murders. Surely life in prison is a good enough reason for her not to confess.
All in all a very interesting programme while there were lots of open questions, trying to find a hypothesis that fitted everything was a great and fun exercise. But ultimate the answer presented, with a bit of thought, was unsatisfactory, with no good reason for the behaviour or actions of many of the characters, other than to deliberately confuse and mislead the audience for dramatic purposes. All in all not up to the level of the best Scaninoir.