WARNING - CONTAINS SPOILERS

Half the fun of this series of Line of Duty has been the crescendo of conspiracy theories surrounding it, fuelled by the way creator Jed Mercurio has skilfully kept tapping into the LoD mythology built up over the preceding five seasons. Craig Parkinson, aka the evil Dot Cottan from earlier series, has been hosting the Obsessed With… Line of Duty podcast, exploring secrets, theories and myths surrounding the show.

As Line of Duty aficionados debate the identity of H and wonder who DCI Joanne Davidson shares her DNA with, this new three-part series from BBC Two investigates the history of real-life corruption in the Metropolitan Police.

DI John Major (Daniel Mays) has been dead a year, shot in the line of duty, though we’re far from that series in terms of tone. Now he’s back at the London Met, artificially augmented, but not very intelligently. If anything he’s a bit more shit than he was before, as one of those involved in the shooting observes.

The porn was a bit disappointing, was it not? Dear old Ted, no longer romantically active, admitted to being a user. The Superintendent Hastings fanclub sighed for sorrow to witness him toss away his status as an essentially decent heartthrob for the Saga generation. Sorry for your loss, ladies. It was also disappointing because the high-risk act of wiping his laptop turned out to have such a bathetic explanation. The 50k lying around in a brown envelope he clearly deemed to have less pressing potential for embarrassment.

Cop a load of that, then. Hana Reznikova is serving time for triple murder. Ted Hastings is on permanent gardening leave. The Huntleys have renewed their wedding vows on a family trip to Disneyworld. Just kidding. This is a Reg 15 alert to advise you that the following paragraphs contain almost nothing but spoilers.

Now promoted to the exhilarating landscapes of BBC One as a reward for previous good behaviour, Line of Duty set off at a scorching pace into the murky shadowland where crime, punishment, ambition and corruption mingle treacherously.

At the end of last year’s third series of Line of Duty, we saw the back of the reprehensible Dot “The Caddy” Cottan, and with the much-abused Keeley Hawes consigned to the show’s morgue of deceased leading characters it felt as though important matters had come to a close. I was dubious about LoD when it began in 2012, but what has gradually become apparent is that its mastermind Jed Mercurio (pictured below) has been playing a long, labyrinthine game.

At last, after three series, Line of Duty delivered a denouement that felt like a satisfying jackhammer to the solar plexus. In the first series the bent copper under investigation escaped justice by jumping in front of a lorry. In the second there were more loose ends than are generally produced by a rope factory. It turns out that patience is a virtue and we should all have had faith.

Two years after its brilliant second series, which put Keeley Hawes's DI Lindsay Denton through the wringer with harrowing intensity, Jed Mercurio's bent-coppers drama is back. This time it's Daniel Mays, as Sgt Danny Waldron, sitting in the crosshairs of Ted Hastings and his AC12 anti-corruption team.

If nothing else, this second series of Jed Mercurio's brutalist police thriller has done wonders for Keeley Hawes. Not that she was in much need of a career pick-me-up, but the way her haunted portrayal of the much-abused DI Lindsay Denton has brooded over the story like a funeral shroud deserves to land her a few gongs and is doubtless already bringing in heaps of job offers.