Blimey. When we said last week that we thought things were going to get a lot darker, we didn’t think it’d happen so fast, or so brutally, but by the end of Episode 2 everything has taken a turn for the terrible. And it makes for compelling viewing.

Even before the shocking home invasion in the final minute, Line of Duty had been doing a sobering job of showing that police work is about as pleasant as a long soak in a septic tank – a division between being trapped in a paper prison of bureaucracy and form-filling, and being thrust out onto the streets to be subjected to more public abuse than a shit Britain’s Got Talent contestant.

A strong supporting cast and some grim location work gives us a sadly accurate portrait of the reality of policing and of the relationship between the law and the lawless in ‘Big Society’ Britain. A child stealing the shoes off a corpse, tweenage hoodies tormenting pensioners, police cars being pelted with anything not bolted down on a council estate… Looking at the hopelessness and tedium of the quota-filling war on street crime, you can actually understand why DCI Tony Gates (Lennie James) only chases the big, sexy cases.

But Gates’ days of being the self-described king around the station are numbered. Beyond the walls of his concrete palace he’s an ordinary family man of weak will – felled by lust for perpetually watery-eyed murderer Jackie Laverty (Gina McKee), his constantly vibrating phone threatens to cause his world to crumble around him.

It means that while Steve Arnott and Kate Fleming (Compton and McClure) have the not particularly thrilling chore of chasing the numbers and untangling the twisted web of laddering and laundered money, the episode’s most powerful scenes are being shared between James and McKee as their passions and weaknesses lead them down a dark path.

And just when you thought that Tony arresting Jackie, and their emotional car ride, would be the most dramatic moment of the hour, along comes a stunning cliffhanger, as three masked men break into Jackie’s home and slit her throat, before placing the knife in the unconscious Tony’s hand. Far from being just a shocking development, it creates a seemingly inescapable predicament for Gates, and leads us to wonder just how desperate a man with so much to lose will become…

Two episodes in and writer Jed Mercurio has already crafted a police drama that feels as claustrophobic and threatening as a night sharing a cell with a convict and his dog.

Three episodes remain and the quality shows no sign of dipping. If you haven’t yet started watching Line of Duty, well, you know where the iPlayer is.

Aired at 9pm on Tuesday 3 July 2012 on BBC Two.

> Order Series 1 on DVD on Amazon.

What did you think of the episode? Let us know below…