Line of Duty: Everything that happened in series one
The first series aired in 2015
Last updated 19th Nov 2025
Jed Mercurio's Line of Duty is one of the most popular crime dramas of the last decade, with six series to date and a seventh coming in 2026. The hit series, which originally started life on BBC Two, follows corruption in the police as Anti-Corruption Unit 12 (AC-12) attempt to fish out the 'bent coppers' who are working alongside organised crime groups in the city.
With cast members Adrian Dunbar (Ted Hastings), Martin Compston (Steve Arnott), and Vicky McClure (Kate Flemming) all returning for series seven, we thought we'd take an extensive look into series one. Be warned - SPOILERS AHEAD.
What happened in Line of Duty season one?
Series one begins with a high-octane police raid on a flat, with DS Steve Arnott instructing the armed-response team to make an arrest on a specific flat. However, when the door numbers get mixed up, a raid on the wrong flat leads to the death of an innocent man. When DS Arnott refuses to cover up the mistake alongside the rest of his team, he's taken in by AC-12, with Superintendent Ted Hastings identifying him as the perfect man for the Anti-Corruption Unit.
DS Arnott's first job involves investigating DCI Tony Gates, a well-respected senior officer who has a high number of successful cases on his CV. Viewers quickly discover DCI Gates isn't the perfect officer after all, as he agrees to cover up a hit-and-run murder for his mistress Jackie Laverty, a woman who is heavily involved in suspicious financial activities.
Acting undercover to help bring him down, DC Kate Fleming joins DCI Gates' team, working alongside DS Matthew "Dot" Cottan and his right-hand man DC Nigel Morton.
As evidence begins to unfold and the body of Jackie's accountant is found by a dog walker, DCI Gates becomes increasingly entangled in covering up her actions, with DS Arnott and Superintendent Hastings working hard to unsettle his team. When DCI Gates handcuffs Jackie and threatens to hand her in, she manages to talk him out of it, inviting him back to her house for the pair to continue their affair. However, they are interrupted by a knock at the door, and Jackie's throat is brutally split by a gang in balaclavas.
When DC Arnott arrives, Jackie's body has been removed from the scene, with DCI Gates pretending he'd just arrived to find she was missing, leaving DC Arnott increasingly suspicious.
As pressure mounts on DCI Gates by AC-12 and also 'The Caddy' crime group he's working for, he's forced into increasingly compromising situations, with AC-12 suspecting he's being manipulated by the OCG.
When he finds his family dog dead in the kitchen, DCI Gates is forced to admit his affair with Jackie to his wife, attempting to protect his family while fending off both AC-12 and the criminals.
The series finale brings the story to head, with DCI Gates agreeing to help AC-12 expose the OCG. As DCI Gates kidnaps The Caddy in his car, he attempts to get him to speak whilst wearing a wire, with DC Arnott and DI Fleming listening in from another vehicle. DCI Gates succeeds in his mission, leaving The Caddy in the car to be arrested by AC-12, but the story doesn't end there...
Speaking to DC Arnott on a busy road, DCI Gates admits he knows he will be dismissed by the police, instead choosing to step in front of a moving lorry, in order to die in the 'Line of Duty' and protect his family.
The series ends with The Caddy being handed over to DC Cottan, but it's quickly made clear he's also in on the corruption, setting up a second series nicely.
Check out the trailer for Line of Duty series one below:
When did it air?
The first ever episode of Line of Duty aired on 26th June 2012, running for five weeks until 24th July 2012.
What channel was it on?
Series one of Line of Duty aired on BBC Two, it wasn't until series four when the show moved to BBC One, after becoming the highest-rated series on BBC Two in 10 years.
How many episodes?
The first series is made up of five episodes.
How many viewers?
Series one averaged 3.80 million viewers.
Who was in the cast of the first season?
Series one introduces viewers to AC-12 officers DS Steve Arnott, DC Kate Fleming and Superintendent Ted Hastings, played by Martin Compston, Vicky McClure and Adrian Dunbar respectively.
The first series also includes other high profile actors such as Neil Morrissey (Men Behaving Badly), Lennie James (The Walking Dead), Craig Parkinson (Grace) and Gina McKee (Bodyguard).
Check out the cast list for series one of Line of Duty below:
Martin Compston as DS Steve Arnott
Vicky McClure as DC Kate Fleming
Adrian Dunbar as Superintendent Ted Hastings
Lennie James as DCI Tony Gates
Craig Parkinson as DS Matthew "Dot" Cottan
Neil Morrissey as DC Nigel Morton
Gina McKee as Jackie Laverty
Paul Higgins as Chief Superintendent Derek Hilton
Owen Teale as Chief Inspector Phillip Osborne
Brian McCardie as Tommy Hunter
Nigel Boyle as DI Ian Bucklles
Kate Ashfield as Jools Gates
Heather Craney as DI Dot Carlyle
Tommy Jessop as Terry Boyle
Faraz Ayub as PC Maneet Bindra
Brian Milligan as DS Jayne Akers
Richard Pepple as DS Kyle Ferringham
Gregory Piper as Ryan Pilkington
You can find an overview of the Line of Duty cast right here.
Can I watch it?
You can watch Line of Duty for free on BBC iPlayer now. The series is also available for customers of streaming service Netflix.
Who wrote it?
Jed Mercurio is the genius behind Line of Duty! Not only did he write and create the series, he also serves as an executive producer on the show.
As well as series one, Jed is involved in the other five series, as well as other popular shows such as Trigger Point and Bodyguard.
Check out which other TV shows Jed Mercurio has worked on.
Where was it filmed?
Filming for series one of Line of Duty took place over 11 weeks in Birmingham, England.
Some notable locations featured in series one include New Street, the old Central Fire Station on Lancaster Circus, Heartlands Parkway, and the historic pub Queen’s Arms on Newhall Street.
The former Municipal Bank building on Broad Street was also used for AC-12's office.
Check out all of the Line of Duty acronyms explained below:
OCG - Organised Crime Group: Serious crime planned, coordinated and conducted by people working together on a continuing basis, mostly acting in different roles depending on their skills and expertise.
PACE - Police and Criminal Evidence Act: Established in 1984, a code of practice that regulates police powers and protects public rights.
REG 15 - Regulation 15 notice: A notice that advises an officer that a complaint has been made or a conduct matter has come to light that warrants investigation by professional standards department.
RIPA - Regulation of Investigatory Powers Act 2000: An act of Parliament of the United Kingdom, which regulates the powers of the public bodies to carry out surveillance and investigation, and covers the interception of communications.
RTC - Road Traffic Collision
ANPR - Automatic Number Plate Recognition: Technology is used to detect, deter and disrupt criminality at a local, force, regional and national level.
AC-12 - Anti-Corruption Unit 12: A dedicated unit that holds responsibility for investigating corruption within the police force.
CHIS - Covert Human Intelligence Source: A person who establishes or maintains a personal or other relationship with another person for the covert purpose.
AFO - Authorised Firearms Officer: A police office, who has been selected, trained, accredited and authorised by their chief officer to carry a firearm operationally.
ARVs - Armed Response Vehicles: ARVs are crewed by Authorised Firearms Officers to respond to incidents believed to involve firearms or other high-risk situations.
DIR - Digital Interview Recording: Digital device used to record police interviews.
IOPC - Independent Office for Police Conduct: A non-departmental public body in England and Wales which, since 8 January 2018, is responsible for overseeing the system for handling complaints made against forces in England and Wales.
FI - Forensic Investigator: The FI gathers and preserves physical evidence at a crime scene to take to a lab where they examine what they or other law enforcement personal have found.
I.P. Address - Internet Protocol Address: A numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication.
SFC - Strategic Firearms Commander: The SFC has overall strategic command of firearms operations, with responsibility and accountability for directions given.
UCO - Undercover Operative: A method use by law enforcement and intelligence agencies. They wear civilian clothes that fit in to avoid detection.
TFC - Tactical Firearms Officer: A TFC provides guidance on the appropriate use in respect of different tactical options involving the deployment of AFOs.
VPN - Virtual Private Network: The extension of a private network that includes links across shared or public networks, such as the Internet.
Now read:
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Your ultimate guide to Line of Duty
Line of Duty: What do all the technical acronyms really mean?