Line of Duty series 5, episode 4 review: Jed Mercurio blows his thriller sky high

We’re halfway through a ratings-smashing Jed Mercurio thriller and, blimey O’Riley, he’s just killed off the most interesting character. As it was with last year’s Bodyguard and the prematurely detonated Julia Montague, so it is with Line of Duty season five and crusading undercover copper John Corbett.

Montague’s death was via cheeky exploding suitcase (or was it? – there were so many twists that by the end it was impossible to recall clearly). Corbett (Stephen Graham), by contrast, has to make do with a more low-tech knife across the throat at the conclusion of another absurdly suspenseful LoD episode.

An even bigger difference is that, unlike Bodyguard and the “is Lavender alive?” chatter, here there is surely no room for ambiguity. The trap is sprung as Corbett’s gangland pal Lisa McQueen (Rochenda Sandall) pretends to be sad about the emergency supply of prostitutes his crew has just shipped in.

Corbett, sensing her distress (she’s PRETENDING, John), grabs a gun and charges out to rescue the “livestock” (do human traffickers really speak like that?).

This is the perfect excuse for McQueen to calmly pop up behind and plunge the blade (though weirdly she starts blubbing in private immediately afterwards). Down Corbett goes, expiring in an ever-expanding slick of blood. The life force has drained out of him faster than Manchester City’s in a Champions League quarter-final. So step away from that Reddit thread. Corbett has been violently expunged beyond reasonable doubt (“VEBRD”, as the acronym-addicted Mercurio would probably insist we call it).

His exit is the biggest shock in an hour piled high with now familiar – are we allowed say “hackneyed”? – Line of Duty twists. Back at AC-12, it’s once again a case of more Hastings less speed, as the previously upstanding Superintendent Ted (Adrian Dunbar) continues to behave more shadily than a lampshade salesman at the start of national lampshade week.

One loose end quickly tidied away is the suggestion – always implausible – that bent, very dead policeman Les Hargreaves was criminal mastermind “H”. He was reeled into the gangland conspiracy only a few months previously (McQueen and company were blackmailing him over his frequenting of their vice den). Which means he’s too new to the game to be “H”, conclude DI Kate Fleming (Vicky McClure) and DS Steve Arnott (Martin Compston).

Light is also shed – rather redundantly it transpires – on Corbett and his Northern Ireland background. He spent his early life in Belfast. And so was, of course, responsible for the paramilitary-style torture of Hasting’s wife (the entire population of Northern Ireland being obviously versed in entry-level paramilitary torture).

With the help of a little bit of kneecapping, Corbett manages to glean from Róisín Hastings that her husband is up to his big bushy eyebrows in debt. Corbett throws this nugget to Arnott during their hilarious broad daylight armed stand-off (doesn’t anyone notice two men holding guns to each other’s heads shouting their lungs out?).

He also promises to reveal the location of a meeting he has set up with “H”. It’s enough for Arnott to disobey a direct order from Hastings to shoot the gone-rogue Corbett. Confused? Join the AC-12 club. They are by this point completely befuddled by Hastings’ suspicious behaviour – if he furrows that brow any deeper it’s going to pop out the back of his head – and by Corbett’s descent into violent paranoia (not that this is going to be an issue going forward).

The only one keeping it together, oddly, is Hastings. He scarcely breaks a sweat as he pretends to be “H” when communicating with Corbett via a fake computer link rustled up by the nerds in police IT.

Obviously, this is supposed to further implicate Hastings. But unless Mercurio is playing a cunning triple-bluff it is undoubtedly a misdirection. So who could the real “H” be? Excluding Hastings means suspicion can potentially fall on literally every other person appearing on screen this season. Lisa McQueen, dodgy lawyer Gill Biggeloe, Corbett’s wife, Corbett’s two adorable kids… with Mercurio all options are open.

What is clear, however, is that with Corbett out of the picture Line of Duty season five, like Bodyguard before it, is about to shapeshift into a very different show. The real excitement will be in discovering how Mercurio reassembles the pieces having just blown his thriller sky high.