Line of Duty returns on Sunday - here's a clip from the first heart-stopping episode released today and 10 things you can expect from AC-12 in series five.

On Sunday, Line of Duty will return for its fifth series, once more dropping viewers into the depths of the morally murky world of police corruption - and having just seen this edge-of-the-seat clip, we can't wait.

For four series, the anti-corruption officers of AC-12 – DI Kate Fleming (Vicky McClure), DS Steve Arnott (Martin Compston) and Detective Superintendent Ted Hastings (Adrian Dunbar) – have had their work cut out for them about clamping down on 'bent coppers', unravelling a network with links to organised crime in the process, all led by a shadowy overlord – also, supposedly a very senior police officer – known only as 'H'.

Written by Jed 'Bodyguard' Mercurio, AC-12's top trio of Hastings, Fleming and Arnott are back along with Maneet Bindra (Maya Sondhi), Gill Biggeloe, Roisin Hastings, DS Sam Railston and Lester Hargreaves will also be back and Stephen Graham as John Corbett will become the team's latest person of interest

Series five kicks off with three police officers 'killed in cold blood' after a transport is hijacked by armed men in balaclavas – a hijack that would have required a police insider. It hands AC-12 a chance to 'crack the highest-level corrupt officers and the top man'. That top man being the mysterious 'H'.

Eastern Daily Press: Balaclava gang - Miroslav (TOMI MAY), McQueen (ROCHENDA SANDALL), Corbett (STEPHEN GRAHAM), Ryan (GREGORY PIPER), Lee (ALASTAIR NATKIEL) - (C) World Productions - Photographer: Aiden MonaghanBalaclava gang - Miroslav (TOMI MAY), McQueen (ROCHENDA SANDALL), Corbett (STEPHEN GRAHAM), Ryan (GREGORY PIPER), Lee (ALASTAIR NATKIEL) - (C) World Productions - Photographer: Aiden Monaghan (Image: WARNING: Use of this copyright image is subject to the terms of use of BBC Pictures' Digital Picture Service (BBC Pictures) a...)

As we plunge back into the action after series four, will Steve recover from his injuries? Is Kate's stint undercover over? What has happened to Maneet? Should we believe that ACC Hilton is 'H' or is it Hargreaves? Or Hastings?

The stage is set for another scintillating series for one of Britain's best ever crime dramas, but just what can be expected from Line of Duty's return?

1) The scariest series yet: According to Martin Compston – the man stepping back into Steve Arnott's signature waistcoat once again – this will be the scariest series of Line of Duty yet. What exactly does that mean? No idea! But it's not long until we get to find out.

2) AC-12's most dangerous adversary: Pitting AC-12 against their most fearsome villain to date –Stephen Graham's (This Is England, Boardwalk Empire, Save Me) John Corbett, otherwise known as 'balaclava man' – may very well be a large part of Line of Duty 5's scare factor. Again, according to Compston, Corbett is 'the most dangerous guy we've come up against by far'. Having come up against some formidable foes such as Lennie James' DCI Gates, Keeley Hawes' DI Denton, Craig Parkinson's DI Cottan and Thandie Newton's DCI Roz Huntley already – that is some accolade.

Eastern Daily Press: Detective Sergeant Steve Arnott (MARTIN COMPSTON), Detective Sergeant Kate Fleming (VICKY McCLURE) , Superintendent Ted Hastings (ADRIAN DUNBAR), Corbett (STEPHEN GRAHAM) - (C) World Productions - Photographer: Aidan MonaghanDetective Sergeant Steve Arnott (MARTIN COMPSTON), Detective Sergeant Kate Fleming (VICKY McCLURE) , Superintendent Ted Hastings (ADRIAN DUNBAR), Corbett (STEPHEN GRAHAM) - (C) World Productions - Photographer: Aidan Monaghan (Image: WARNING: Use of this copyright image is subject to the terms of use of BBC Pictures' Digital Picture Service (BBC Pictures) a...)

3) Bold new territory: Jed Mercurio has promised that this new series will step into 'very fresh territory' - expect characters never seen before. Expect things never done before. Expect evolution. The series will see Mecurio's scripts stepping out of the realm of cops against cops and delving a little more into flat-out cops versus crime with 'balaclava man' and his 'balaclava gang' taking on the role of villains.

4) But Ted, surely, will still say something about 'bent coppers'? Rather like Steve's waistcoats, Ted Hastings' one-liners are a staple of the series with none more iconic than his interest in catching 'bent coppers'. It is not a Line of Duty series without Ted name-dropping the officers he finds most offensive of all* (*or is he protesting TOO MUCH?).

5) It will become the talk of the nation: The captivating cop drama has rode atop a tsunami of growing popularity since its initial debut, way back in 2012. It wears the crown for the most popular drama series broadcast on BBC Two in the multi-channel era – so much so, it now airs on BBC One. To put it in perspective, Line of Duty's first episode had 3 million viewers while its latest – the series four finale – had 10.4 million. Come Sunday, it will take over once more – dominating social media and becoming the talk on the bus, the hairdressers, the dentists, the doctor's surgery waiting rooms…move over Brexit, the nation's latest small screen obsession is almost here.

6) The unexpected: As evidenced by his other series, Bodyguard, Jed Mercurio is pretty good at keeping an audience on its toes. And he knows how to keep his actors on their toes, too, according to Adrian Dunbar. The man who masterfully portrays has revealed that one of the first things to do when getting a new script from Mercurio, is to 'check that you're not dead'. Expect the unexpected at all times, especially as Mecurio has said that he would 'definitely' kill off one of the main trio if he thought the story was leading in that particular direction.

7) Intense interrogation scenes: Surely some form of black magic is involved in Mercurio's ability to make lengthy interrogation scenes – a few people sat around a table – as engrossing as he does. Like the waistcoats and the 'bent coppers' and the twists, it just wouldn't be Line of Duty without a long interrogation scene in which AC-12 sit someone down and carefully dismantle them, piece by excruciating piece. Or, vice versa. Regardless of how it plays out though, it is impossible not to be captivated from start to finish and edge ever closer to the edge of your seat.

8) Smashing gender stereotypes: Line of Duty has always had a great female cast and this series appears to be no different. Vicky McClure is back as the ever-brilliant Kate Fleming – renowned for stints in undercover roles and just general badassery. She will be joined by Rochenda Sandall (Broken, Coronation Street) as Lisa McQueen, part of the balaclava gang while Susan Vidler of Trainspotting, Shetland, Doctor Who and more is onboard as a reportedly formidable, DSU Powell. After the likes of Keeley Hawes and Thandie Newton in previous series, expect them to leave quite the impression.

9) A podcast for the obsessed: The BBC has announced a podcast for fans which will run alongside the show, providing extra insight and offering a virual water cooler to fill the gap before you can talk to real life humans about Sunday night's action. 'Obsessed With…Line Of Duty' will provide post-episode chat from comedians and Line of Duty super-fans Lolly Adefope and Brett Goldstein along with reporter Lauren O'Neill and special guests including celebrity fans and members of the Line Of Duty team to tease out the clues, delve into each conspiracy theory and explored every aspect of the show.

10) There will be more: After what will surely be a scintillating ride for six, intensity filled episodes, rest assured – Mercurio and the AC-12 team will be back for another series, pencilled for 2020. In the case of the tremendous trio, that's as long as they are A) all alive and B) have not been found to be corrupt. You honestly never know with Line of Duty.

* Series five starts on Sunday at 9pm on BBC One.