Series 3 consists of six episodes and originally aired on BBC Two between 24 March 2016 and 28 April 2016.
- Daniel Mays as PS Daniel 'Danny' Waldron
- Martin Compston as DS Steve Arnott
- Vicky McClure as DC Kate Fleming
- Adrian Dunbar as Supt. Edward 'Ted' Hastings
- Craig Parkinson as DI Matthew 'Dot' Cottan
- Shaun Parkes as CS Terry Reynolds
- Asher Ali as PC Harinderpal 'Hari' Bains
- Leanne Best as PC Jacqueline 'Jackie' Brickford
- Will Mellor as PC Roderick 'Rod' Kennedy
- Lisa Palfrey as Insp. Tracey McAndrew
- George Costigan as Former CS Patrick Fairbank
- Keeley Hawes as Former DI Lindsay Denton
- Aiysha Hart as DS Samantha 'Sam' Railston
- Neil Morrissey as DC Nigel 'Nige' Morton
- Maya Sondhi as PC Maneet Bindra
- Polly Walker as Gill Biggeloe
The third instalment of Line of Duty saw Daniel Mays’ character Danny Waldron at the centre of AC-12′s latest investigation, as they discovered how his story intertwined with that of The Caddy and Tommy Hunter.
Armed response leader Sergeant Danny Waldron was the main suspect of AC-12′s investigation in series three. It kicked off with a raid that ended in Waldron gunning down a suspect, Ronan Murphy, in cold blood, before convincing his team to make it look as if the dead man was shot first.
AC-12 became suspicious about Waldron’s answers when they brought him in to question him, and DC Kate Fleming was subsequently placed undercover on his team as PC Kate Francis.
Waldron later lurked at the funeral of the man he killed, and followed one of the mourners, Linus Murphy, before breaking into his home and holding him at gunpoint. During the showdown, it was revealed Linus and Ronan had abused Waldron as a child while he was living in a children’s home (Sands View Boy's Home). Waldron killed Linus and returned to his flat, leaving a list of names, which also included the murdered gangster Tommy Hunter (aka, the one The Caddy had killed in series two), in an envelope addressed to DS Steve Arnott.
Returning to work, Waldron led a drugs raid, during which Fleming was ordered to stay behind as the rest of his team looked upstairs at the property. But after gunshots were fired, Fleming walked into the room to find Waldron had been shot, as the rest of his team stood around him. He later died, and the rest of his team claimed he killed himself.
During an inspection on Waldron’s house, AC-12 connected him to Linus and Ronan Murphy’s murders, while DI Matthew Cottan (aka The Caddy) found the list of names and stole it.
When another of Waldron’s team was found dead in a warehouse, the two remaining officers, PC Hari Bains and PC Jackie Brickford, changed their story and claimed the now deceased PC Rod Kennedy killed Waldron. It was later revealed Bains was a corrupt officer who had killed Waldron under the instruction of The Caddy.
Meanwhile, imprisoned corrupt officer Lindsay Denton had been appealing her case following the events of series two. It was overturned when she revealed she had sex with Arnott while he was undercover, thus exposing AC-12’s failings in their investigation into her.
By this point, AC-12 had connected Waldron and Murphy to Sands View boys’ home, and were on the case of a paedophile ring. Determined to make her way back into the force after her release from prison, Denton agreed to assist Arnott on the case.
Elsewhere, worried about being exposed, Cottan began trying to pin evidence on Arnott that would point to him being The Caddy.
Arnott and Denton then investigated the possibility that Waldron kept a digital copy of his list of abusers, and after tricking Arnott into pursuing a false lead, she sloped off to hack into Waldron’s emails. In his account, she found a photo of the list and sent it to herself, wanting to use it as insurance for her to return to the police force.
However, while at the internet cafe, she was tracked down by Cottan, who summoned her to his car – which actually turned out to be Arnott’s service vehicle but with false number plates. After driving Denton to an industrial estate, Cottan showed his true colours and attempted to blackmail her at gunpoint into sending him the list. After she didn’t agree, he shot her dead, but it turned out she had already sent the list to AC-12.
With the evidence now stacked against him thanks to Cottan’s cunning work, Arnott was arrested for Denton’s murder and on suspicion of being The Caddy.
Fleming then revealed she had actually been undercover investigating her own department under authorisation from Supt. Madeline Summers at AC-3, and had noticed some inconsistencies in Cottan’s line of questioning while interview Arnott, and began to gather evidence against him.
Eventually, Cottan was brought in for questioning. He initially denied all knowledge when presented with the evidence, but soon unmasked himself as The Caddy. In dramatic scenes, an armed guard in AC-12′s offices turned his gun on members of the team before shooting through a pane of glass in the interview room, allowing Cottan to escape.
Then followed a tense chase scene, where Fleming pursued Cottan, who had escaped in a getaway car. After managing to shoot the driver, she went to confront Cottan, but as passenger in the vehicle fired shots at her, Cottan stepped in to take the bullets.
Fading away, Cottan recorded a dying declaration that lead to the conviction of a police officer – Former Chief Superintendent Patrick Fairbank – who had been involved in the paedophile ring. However, this dying declaration would become even more important in series four, and was revisited in series five...
7 August 1995 - Patrick Fairbank, Dale Roach and Jimmy Saville are photographed together
14 March 1997 - Patrick Fairbank and Dale Roach are working together and interact with Sandsview boys home
19 September 1998 - Oliver Stephens-Lloyd submits a list of names of abusers at Sands View to Fairbank
14 November 1998 - Oliver Stephens-Lloyd found dead at the Jetty
21 November 1998 - A report was issued on the apparent suicide of Oliver Stephens-Lloyd
2008 - Patrick Fairbank retires from the police force
17 November 2012 - Ronan Murphy first brought in for questioning by Murder Squad
21 March 2013 - Ronan Murphy last interviewed by Murder squad
21 May 2015 - Dot and Steve interview Hari at his house
1 June 2015 - Tower Block drugs raid
7 June 2015 - Linus Murphy Death, Danny Waldron's Death
7 July 2015 - Steve and Kate interview Patrick Fairbank at this house
13 July 2015 - Danny Waldron's Funeral, Steve gets issued a Glock from South Ferry
17 July 2015 - Lindsay Denton is murdered
18 July 2015 - The Caddy is shot dead