The main trio of Policemen at AC-12 (anti corruption 12): DS Steve Arnott (Arnott), DC Kate Fleming (Kate) and Superintendent Ted Hastings (Ted) - Investigate DCI Tony Gates (Gates).

Tony Gates has some suspiciously good arrest numbers and is shagging a wealthy gangster money launderer Jackie Laverty. While he is at her house she gets murdered by gangsters and Tony's finger prints are placed at the scene so that the gangsters have a tame policeman. Tony is also in the shit because he tries to cover up Laverty running over a dog but it turned out to be a person, who also happened to be Laverty's accountant.

The gangster ringleader is Tommy Hunter who has actual bent coppers inside Tony Gates police team - "Dot" Cottan and Neil Morrisey. Dot Cottan is known as "the caddy" and has a similar relationship to Tommy hunter that Matt Damon has with Jack Nicholson in The Department - a young man is groomed by a gangster and rises up the ranks of the police.

In the pursuit of finding and arresting Tommy Hunter, Tony Gates dies "in the line of duty" - (this is an engineered suicide) so his wife and family can get his pension.

Tommy Hunter goes into witness protection and Dot Cottan gets transferred to AC-12.

Newly introduced to the team is Georgia Trotman

DI Lindsey Denton organises the transport of witness protectioned Tommy Hunter except the whole thing ends up being a complete cock up ending up with Tommy Hunter and a police woman dead.

Newly introduced to the AC12 team is Georgia Trotman. Arnott and Trottman enter into a relationship and then while investigating a suspicious nurse Trotman gets thrown out of a window.

Lindsey Denton is a pretty good fucking police but she has a shit life and crippling mortgage. Upon the investigation of the cock up she gets transferred to missing persons investigations and fixates on a girl named Carly Kirk

Another policeman  DCC Mark Dryden - Denton's boss and aware of the the transport operation - gets into a right mess because he passes his speeding points to his wife.

the police woman who died at the transport was actually murdered because she was the one who informed gangsters about the route for a large sum of money. She also kept recordings of Tommy Hunter ranting about Bent Coppers including "the caddy".

here's how it all wraps up:

Prior to the car incident cock up Denton notices her boss Dryden at a party and starts flirting and getting sexually involved with Carly Kirk. Carly is then beaten by Tommy Hunter and as Denton tries to get involved the police woman stop him, she is the witness protection liason and Hunter is in some "above law" status because he can grass on a lot of gangsters. But later on the liason meets with Denton with a proposal -

Make a ton of money by leading Tommy Hunter back to some gangsters when he gets transported - he's a piece of shit that gets "dealt with" and Lindsey makes some money and Carly will get a quantum of justice.

Denton is arrested for conspiracy to murder
Dot Cottan gets a commendation.

Danny Waldron's shooty police team chase after baddies, in one particular raid Danny chases a criminal to an alley and even though the criminal gives up his weapon, Danny shoots him and makes it look like he was attacked, his team join to make it look as though there was a lot of shooting. - this prompts AC-12 to investigate him
It turns out that Danny was molested as a child in a childrens home and the criminal he shot was part of that structure and he did so in revenge and has a list of people - addressed to arnott - who were part of the abuse.
Before there are further investigations Danny is found shot and dying upstairs in a raid gone wrong.

For some reason Dot Cottan starts screwing up the investigation and burns the list.

Denton (in prison from last year) appeals her conviction by saying she had a sexual relationship with Arnott- jeopardising the murder case against her and she is found not guilty.

Denton's release causes a lot of problems for Dot Cottan as (I think) she can link him to Hunter.

Dot Cottan sees the walls collapsing around him, but - unlike Trump,  these are actually going to cause him problems. He tries to frame Arnott as "the Caddy".

Cottan murders Denton in Arnott's stolen car because she has obtained a digital copy of the list that Cottan destroyed earlier. Luckily for the investigation (if not Denton) she has managed to send the copy to Ted.

A lot of investigation however leads Fleming to work out that Cottan is the bent cop amongst them and they arrest the bastard!

But because of his connections he gets an exit which involves armed police within AC-12 shooting the place up and busting him out.

However fleming gets onto the chase and Cottan ends up shot and makes a "dying declaration" which results in arrests relating to the child abuse that Waldron was trying to avenge.

Roz Huntley is ignoring a Forensic Scientist's assertions that a serial killer suspect is definitely innocent in the face of pressure to arrest the serial killer suspect. The FS calls AC12 as he suspects bentness. Roz goes to his house and they get into a fight and she damages her hand and then gets knocked out. The FS tries to chop her up and dispose of her body because he thinks she's dead. But she's not. Then she accidentally kills the guy. In the act of covering up the killing she creates a big mess for herself.

During AC12s investigations Arnott is attacked by a "balaclava man".

The OCG meets up with the Do-Re-Me it's as Easy as ABC, 1,2 3 baby you and me.

Organised Crime Group is run by Undercover Officer DS Corbett (yeah hmm). But principally this year is about finding out the biggest bent cop - H - referenced by Hunter in his ranty video and Dot Cottan in his dying death statement. In the process of the investigations Corbett is murdered.

There's a little bit to suggest it might be Hastings, but really the big bad is actually a police lawyer called Biggeloe. The one wrinkle is that Hastings has £50k found amongst his possessions but these are explained away satisfactorily for the investigations. The big problem though is that the 50k was actually from a £100k of stolen money. Hastings gives a whole bunch of money to Corbett's widow.


Is HASTINGS BENT?!

There have been allusions and accusations he’s a mason and or misogynist and or Illuminati.

Upon reviewing a video of dot cottan dying Arnott makes the inference that even though they think all the loose ends are tied up there might actually still be a  bent bigwig on the loose.