Line of Duty series 5, episode 3 review: Jed Mercurio at his most brilliantly manipulative

While logic occasionally somersaults out the window, the show is still like no other on television

Deeper and deeper into Jed Mercurio’s pea-soup plot we plunge as the latest Line of Duty (BBC1) treats us to one action-packed set piece, several tense exchanges and a vaguely shocking twist.

The (mild) surprise is that undercover agent – “UCO” in Line of Duty’s patented copper lingo – John Corbett (a deeply peeved Stephen Graham) has been consumed by his paranoia and now considers everyone an enemy.

In a satisfying cliffhanger to an episode that veers – and this is arguably Mercurio’s trademark – from unintentionally hysterical to unbearably suspenseful, he turns up on the doorstep of Superintendent Ted Hastings’s soon to be ex-wife (Andrea Irvine). He’s brought along gun, bolt-cutters and balaclava (and claims to be AC-12’s Steve Arnott).

No good can come of an undercover policeman on your doorstep with gun, bolt cutters and balaclava. And so it proves as Corbett breaks in and… well, we’ll have to wait until next week. Here we have Mercurio at his most brilliantly manipulative: teasing us with something horrific – Mrs Hastings is presumably about to be bundled off to parts unpleasant – and then cutting dramatically to black.

Also up in the air are the precise circumstances in which on-the-take detective Les Hargreaves (Tony Pitts) has died. Corbett machine guns him in the legs during his gang’s raid on Eastfield Depot, a police lock-up brimming with firearms, confiscated cash and drugs (the explosive set-piece).

Yet later Superintendent Hastings (Adrian Dunbar) delivers to the AC-12 team the sad news that Hargreaves passed away from injuries that initially seemed anything but life-threatening.

Mercurio is by now pointing huge virtual arrows at Hastings implying he is the real “H”: the Dark Lord of Corrupt Policeman pulling the strings all these years. AC-12’s Arnott (Martin Compston) and Kate Fleming (Vicky McClure) at one point reveal to their boss that Corbett has been conversing with H via laptop. In the next scene Hastings is back at his hotel wrapping his own laptop in menacing bubble wrap and taking it off to be destroyed.

We’re obviously supposed to consider him guilty as sin – which, Mercurio being Mercurio, almost certainly means he isn’t. So who could “H” really be? Legal counsel Gill Biggeloe (Polly Walker), who sees out the episode all set for a spot of how’s your father with Ted? Former undercover officer Fleming? A sentient photocopier lingering just out of camera shot all this time?

The thrill of the Mercurio chase, of course, is that all options are on the table. Line of Duty piles bombshell upon bombshell and while it can sometimes feel as if the writer is in an arm’s race with himself, the sheer, gravitation yank of the plot is undeniably irresistible

That’s certainly true of LoD season five, which is posting blockbuster ratings (some 11.4 million tuned in to week two’s instalment). Episode three of six, it is true, doesn’t so much add another square to the jigsaw as throw the pieces up in the air and then grind them into the carpet.

It isn’t always easy to follow and logic occasionally somersaults out the window (surely Corbett should have given himself away as a UCO by cleaning out his gang’s print shop back office immediately before the police raid?). But at full tilt this is a twisting, turning slalom like no other on television.