Her unexpected return set this sensational series alight. But for Line Of Duty’s princess of darkness Lindsay Denton it’s the end of the line.

In an extraordinarily shocking scene, crooked cop Matthew “Dot” Cottan blew the former CID detective’s brains out at point blank range. Bang, he shot her dead. And left her slumped in a blood spattered car.

It’s a tragedy that the fantastically cold and calculating DI Denton won’t be around to bring her sinister charm to next week’s eagerly awaited finale. Until her untimely demise she stole the show.

Although it looks as if she was the victim of a profound injustice, there was something slightly satanic about this shark-eyed woman on a demonic mission to clear her name. “I want justice,” she snarled. “And I don’t care how unjustly I get it.”

In a powerhouse performance, actress Keeley Hawes created a hauntingly charismatic character who wasn’t evil… but was a long way from good. She was magnificently terrifying.

Whatever she did, you couldn’t take your eyes off her. When livid Lindsay kicked the living daylights out of her creep of a parole officer it was one of those memorable moments that make TV violence worthwhile. Let’s face it… we were all cheering.

And now that she’s gone, we’ll all miss her. But at least she bowed out in unforgettable style. Seconds before the fatal bullet, her last deed was to dispatch an incendiary email revealing a list of child-sex shame.

As dastardly Dot ran from the scene of his gruesome crime, the net was already closing in on the VIP paedophiles he served. Stand by for their well-deserved downfall. Hopefully.

The pulsating penultimate episode was packed with the surprise twists and turns we’ve come to expect of this brilliantly compelling BBC2 drama.

Lindsay Denton may have been many things. But when she stared down the barrel of Cottan’s gun and courageously refused his £100,000 hush-money bribe she proved she was incorruptible. Unlike so many of her ex colleagues.

For a while even the doyenne of anti-corruption Superintendent Ted Hastings was in the frame. Damned by a masonic handshake with dodgy retired vice squad chief Patrick Fairbank, a man with a selective memory like a sieve.

And who posed in a friendly photograph with a grotesquely fat councillor bearing an uncanny similarity to the late not-so-great Cyril Smith... and the dreaded Jimmy Savile. Hastings: “Do you recognise this man?” Fairbank: “I think we all do.”

Meanwhile, AC-12’s lawyer Gill Biggeloe has clearly got something to hide. Is this shifty attorney in cahoots with the murderous DI Cottan? Watch this space.

Now the suspended DS Steve Arnott is fighting for his career. And after conniving Cottan used his car to kill Denton in, he’s facing an uphill battle.

Suffice to say that with just one blockbuster instalment to go, there are loose ends to be tied up. Who’s guilty? Who’s innocent? Who knows? When the police are the criminals who can you trust?