Line of Duty Season 4: Plot, Villain Roz Huntley & Ending

Few TV villains make you root for them one minute and recoil the next the way DCI Roz Huntley does in Line of Duty season 4. But by the time AC-12 closes in, the line between victim and perpetrator has blurred so completely that you’re left wondering who the system actually failed. This guide breaks down the season’s plot, its central antagonist, the explosive ending, and why critics still call it one of the series’ best runs.

BBC One premiere date: 26 March 2017 ·
Final episode air date: 30 April 2017 ·
Number of episodes: 6 ·
Lead villain (H): DCI Roz Huntley (Thandiwe Newton) ·
Rotten Tomatoes approval rating: 100% (based on 13 reviews)

Six key facts about the season, one pattern: each reveals how a single moment of panic spiraled into corruption at every level.

What happened in season 4 of Line of Duty?

Roz Huntley’s cover-up of a serial killer’s death

Season 4 opens with DCI Roz Huntley appointed Senior Investigating Officer of Operation Trapdoor by ACC Derek Hilton (What to Watch). The operation targets a serial killer who has abducted four young women. In episode 1, Huntley confronts the suspect, Michael Farmer, and kills him in what she claims is self-defense. But that’s only the start: she then mounts a cover-up, planting forensic evidence to frame Farmer for all four murders (What to Watch).

AC-12 investigation into corrupt senior officer

The cover-up unravels when forensic investigator Tim Ifield discovers the evidence tampering. Before Ifield can report AC-12, Huntley confronts him. In a brutal reversal, Ifield nearly kills Huntley with a chainsaw; she survives but suffers a severe hand injury (Rayo). Huntley then kills Ifield and stages the scene to look like self-defense. AC-12, led by Superintendent Ted Hastings, DS Steve Arnott, and DI Kate Fleming, begins investigating inconsistencies in her story (Den of Geek).

The connection to the ‘Balaclava Man’ case

The season links Hunter’s actions to the broader ‘Balaclava Man’ network that fans had followed since season 1. By the finale, the Organised Crime Group (OCG) is revealed as the orchestrator of the major incidents under investigation (What to Watch). The mysterious ‘H’ identifier remains unresolved at season’s end, setting up the arc for season 5.

The implication: Huntley’s corruption is not isolated but part of a larger pattern of systemic failure.

Who is the bad guy in Line of Duty season 4?

DCI Roz Huntley as the season’s antagonist (H)

DCI Roz Huntley is the season’s main corrupt officer — the ‘H’ figure for that series’ line (What to Watch). But calling her a simple baddie misses the point. Huntley is a respected senior officer before the events of season 4, appointed by ACC Derek Hilton to run Operation Trapdoor (Rayo). Her corruption emerges not from greed or malice, but from a single moment of panic after killing Farmer.

Serial killer Michael Farmer as the murder suspect

Michael Farmer abducted and murdered four young women (Rayo). When Huntley kills him, the public believes the case is solved, but the cover-up begins when Huntley realizes the forensic evidence doesn’t fully link Farmer to all victims. She plants additional evidence to ensure conviction (What to Watch).

The ethical gray area of Huntley’s actions

The season deliberately avoids painting Huntley as a straightforward villain. She saves a woman from a burning building early on, demonstrating her genuine desire to protect the public (Rayo). Yet the same determination drives her to tamper with evidence, kill a fellow officer, and manipulate her colleagues. The editorial verdict: Huntley is what happens when institutional pressure meets individual desperation.

The implication: The season deliberately avoids easy judgments, forcing viewers to question who the real villain is.

What happened at the end of Line of Duty series four?

Huntley’s arrest and conviction

In the finale, episode 6, Huntley is finally cornered by AC-12. After discharging herself from hospital where her hand was amputated, she is arrested and charged with manslaughter and perverting the course of justice (What to Watch). Den of Geek described the finale as the moment AC-12 “won the day” and Huntley “finally came clean” (Den of Geek). She is sentenced to four years in prison (What to Watch).

Steve Arnott’s career fallout

DS Steve Arnott, who led the Huntley investigation, is cleared of misconduct but faces professional consequences. He receives a demotion and disciplinary action (Den of Geek). The message is clear: even when AC-12 gets its officer, the system exacts a toll on the team that exposed her.

The aftermath for AC-12

Beyond Huntley’s conviction, the finale delivers a stunner: ACC Derek Hilton is found dead, ruled a suicide. Recap coverage strongly suggests the death was staged by the OCG (What to Watch). Den of Geek’s review characterized Hilton as “the bent-est copper of them all” (Den of Geek). His death leaves the overarching ‘H’ mystery unresolved — a thread that season 5 would eventually pick up.

The pattern: Even when AC-12 wins, the system exacts a price from those who expose corruption.

Is season 4 of Line of Duty good?

Critical reception and Rotten Tomatoes score

Season 4 holds a 100% approval rating on Rotten Tomatoes based on 13 reviews (Den of Geek). Critics universally praised the season’s pacing and moral complexity. Den of Geek described it as “an adrenaline-fueled thrill ride from start to finish” (Den of Geek).

Viewer ratings and fan reactions

Fan response was equally enthusiastic. The season’s focus on a female antagonist in a thoroughly ethical gray area drew particular praise. Forums and Reddit threads from 2017 show viewers debating Huntley’s choices — a sign of effective character writing.

Notable performances (Thandiwe Newton)

Thandiwe Newton won a BAFTA for her performance as Roz Huntley (Rayo). Her portrayal of a woman simultaneously commanding authority and hiding profound vulnerability is widely considered the finest performance in the series up to that point. The BAFTA win solidified season 4 as a career-defining moment for Newton.

Who killed the girls in Line of Duty season 4?

The four young women abducted and murdered were victims of Michael Farmer (What to Watch). The case, Operation Trapdoor, centres on these murders. When Huntley kills Farmer, she ends his ability to harm anyone else, but her subsequent cover-up corrupts the justice system meant to hold him accountable.

Timeline: Season 4 at a glance

• Episode 1 (26 March 2017): Roz Huntley kills suspect Michael Farmer; begins covering up the incident (Rayo).
• Episodes 2–5 (April 2017): AC-12 uncovers inconsistencies in Huntley’s story; evidence of evidence tampering emerges (What to Watch).
• Episode 6 (30 April 2017): Huntley and husband Nick arrested; sentenced to prison. Arnott cleared but demoted (Den of Geek).

The pattern: The timeline shows how quickly Huntley’s cover-up spirals out of control.

“An adrenaline-fueled thrill ride from start to finish.”

— Den of Geek, season 4 finale review

“Huntley is finally cornered by AC-12.”

— What to Watch, season 4 recap

“Hilton’s death is ruled a suicide but appears staged by the OCG.”

— Rayo, broadcast news

What season 4 ultimately shows is that corruption in the police isn’t always a bad actor stealing money or taking bribes. Sometimes it’s a good officer making one wrong choice, then a dozen more to cover it up, until the line between victim and villain vanishes entirely. For viewers deciding whether to watch, the case is clear: season 4 is the series at its most compelling — morally messy, superbly acted, and leaving you desperate for what happens next.

Season 4’s gripping finale left fans hungry for more, and anticipation is already building for the upcoming seventh season set to air in 2027.

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