Line of Duty fans finally get a proper look at the mysterious balaclava gang in new trailer

And several new characters look to be straying far from the letter of the law: the sneak peek follows a hijacking of a police transport vehicle, with three officers killed in cold blood by a gang wearing balaclavas.

As well as new character John Corbett (Stephen Graham) appearing in the infamous headwear from series four, we also see a glimpse of his criminal associate Lisa McQueen (Rochenda Sandall).

Will they lead us to the corrupt officer behind the outfit whose misdeeds stretch across the last four series?

It's a question for AC-12, but the unit appears to be battling its own problems with Martin Compston’s DS Arnott held at gunpoint and DS Kate Fleming (Vicky McClure) left pulling off her signature shocked face at several points.

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But worst of all, it looks like Adrian Dunbar’s Superintendent Ted Hastings will be under severe scrutiny this series, with the police still searching for a criminal insider, codename ‘H’, on the force. Not only do Hastings and Arnott appear to be at loggerheads in the trailer, but there’s also a very ominous shot of the AC-12 chief in what appears to be a police cell...

Line of Duty is written and created by Jed Mercurio and is “coming soon” to BBC1.

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