A stylish and shocking final episode simultaneously provides a constant ‘end of days’ theme as well as keeping the punishing pace of Prey‘s opening two instalments, juggling dual storylines more than admirably.

Although things got a tad complicated at times, it’s a necessary evil as the stunning third act is allowed due deference to breathe and crowbar in yet more tectonic-shifting revelations. This tense and taut episode is complimented as ever by Nick Murphy’s guerilla-style, adrenaline-fuelled directorial vision, remaining key to the success of this show, keeping the pace punishingly ferocious and, in moments of high emotion, powerful and brazenly simple.

Praise must also be given to Rosie Cavaliero’s portrayal of the imperfect and yet brilliant superintendant Susan Reinhardt. Cavaliero portrays the real struggle that Reinhardt internally battles with throughout, once so confident in being wrong to stepping hesitantly into the light, ending the series a better person all round.

Line of Duty’s Craig Parkinson also excels as the broken Sean, someone considered a villain a few weeks back only to be revealed as a sensitive, troubled and pressured man hiding under all the machismo. Often drunk, and taking the murder of Marcus’s wife Abby and son Max particularly hard, the episode’s finale sees a well-timed shocking reveal of Sean’s potential paternity of Max in the dying moments of the series and indeed, sadly, Sean’s life.

Further acknowledgement of writer Chris Lunt must be given for changing the rules of the game somewhat by creating another character that is female, in a position of power, and totally, utterly and painfully human. Anastasia Hille’s Detective Mackenzie is a villain, a murderer, ruthless and powerful, and a rarity: sympathetic. All she wanted to do was be listened to when she was assaulted by a mafia boss and bully.

The crushing regret and secret that Andrea, played exquisitely by Hille, has had to live with for decades has sent her mad, but in the process made her brilliant at her job in every other way. Taking away the usually male-led aspirations of TV villainy – I Am Top Dog, We Run This City – we instead get an uncompromising and almost plaintive portrait of a tortured and desperate woman pushed to extremes. Women with complications and contradictions. And it is brilliant TV. Who’d have thought?

As the lead of the thing, you may expect John Simm to wear a massive coat and frown, brooding around town, but Simm’s style remains subtle, nuanced and muted with short bursts of frustration and angst.

The overarching sense of some tremendous force being held on a taught leash throughout makes his Marcus a different animal/detective altogether. And for goodness’ sake, Marcus, invest in some gloves; your fingerprints are on everything.

A watershed moment though is the heartbreaking and touching scene with Marcus on the phone to Finn, played gently and sensitively by Ezra Dent-Watson, as they watch a video on Finn’s iPad of the family messing around, making a homemade birthday message. Marcus pledges ‘That’s us, Finn.’ And throughout the reveal in the last act, we still believe it to be.

By the end of this mini-series, you yearn for the happy ending we are rewarded with; the ending that frankly needed to happen.

Aired at 9pm on Monday  12 May 2014 on ITV.