Feeling like a puppy submerged into a bucket of cold vinegar, we watch the emergency transfer of a mystery witness protectionee go catastrophically wrong. (Is it Robert Lindsay, who famously quit the series just two days into filming, trying to smuggle himself back into the show under a blanket? Unlikely, even if this is a show that loves to surprise.)

DI Denton is the only survivor and thus chief suspect, meaning we’re treated to plenty of emoting from Keeley Hawes, an actor who’s like that first cup of Earl Grey on a morning; familiar yet ever so refreshing. Not even an ill-fitting neckbrace constricts her performance as she battles through the entire gamut of reactions provoked by getting a colleague-mandated swirly, bludgeoning an inconsiderate neighbour over the head with a wine bottle, and blabbering through a stressful police interview with DS Arnott (Martin Compston, who’s more of an English Breakfast on the actor/tea scale) and the Anti-Corruption squad.

And as with the last series, it’s the interview scenes where the drama coalesces and writer Jed Mercurio’s dialogue shines, in the manner of a sharp object glinting from the dark. There’s layers of meaning beneath each utterance that give it the feel of pure theatre with a police tape recorder. We could watch a whole hour of it.

Beyond the ‘end of interview’ click, everyone’s favourite dramatic shirehorse Adrian Dunbar looks to have a role of greater depth beyond putting his hands on his hips and asking ‘What were you thinking son, eh?’ as we’re introduced to his troubled marriage. In fact, while the first series kept an eye on the brittle relationships between the police and the public, Series 2 seems to be placing the relationships of the main cast at the fore, including DC Fleming’s (Vicky McClure) relationship with Aker’s husband, and Arnott’s drunken fling with Trotman. Ohh, poor Trotman…

Jessica Raine fans, you may now return to the cosy bosom of Call the Midwife. Unless DC Georgia Trotman performed a Sherlockian feat in falling from that window, she ain’t coming back. On one hand, that’s a shame; Raine is a terrific actress, this was a different role from what the Sunday night crowd are used to, and it looked like there was a genuine plot trajectory for another strong female character. But on the other hand, it’s exciting that this is a show that can so mercilessly kill off a big name.

Much like Jackie Laverty’s death in Series 1, Trotman’s plummet reminds us that the most dangerous place to be in Line of Duty is between Jed Mercurio’s pen and the page. It’ll annoy some, but it’s a reminder that anything can happen, and that kind of unease is a great way to start a series. Especially when one starts off this well.

Okay. Now you can celebrate.

Aired at 9pm on Wednesday 12 February 2014 on BBC Two.

> Buy Series 1 on DVD on Amazon.

> Buy Series 2 on DVD on Amazon.

Watch the Series 2 trailer…

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