After a couple of sluggish episodes that could have been combined into a single much better one, and a chapter that hinted at better things to come, last night’s fourth episode finally delivered on the promise that had been established. Dark and gripping, there still wasn’t much action in the truest sense of the word until the last few minutes, but those appalling conversations in the Cabinet made that episode something special. And after that, you just knew the finale was going to be a humdinger…

Related: Day I review | Day II review | Day III review | Day IV review

Before the episode began, the continuity guy announced that this is ‘definitely not for children’ and how right he was. Day V may not have been particularly gory, but my word it was chilling.

In the same way that seeing Cybermen in ordinary homes was surprisingly terrifying in Doomsday, seeing the government – meant to support and defend its people – send army troops to round up children for little more than glorified junkies looking for their next hit… that’s, as they say, intense. But last time, aliens were the bad guys – this time, the horror is accentuated because it’s man who’s the monster.

But with Captain Jack in custody, apparently having given up all hope, and Gwen on her way back to Wales, deep in mourning, the “process” as the Prime Minister euphemistically puts it gets underway. The first victims? The Frobisher family. What a shocking, gut-wrenching sequence as Bridget Spears explained that John was a good man as he, well, “saved” his children from what he felt was a fate worse than death.

People have had their issues with Russell T Davies, and always will, but for me his greatest strength is that he makes heroes of ordinary people. Shop-worker Rose is a great example of course, but also the populous returning strength to a weakened Doctor just by believing, or the rotund kid at school who saves his classmates from the Krillitane. And now Bridget, Lois, the local bobby fighting back against “maximum force”, and the fathers of the very “undesirables” being taken away. Wonderful stuff.

The denouement however, I’ve yet to make up my mind about… Jack using his own grandson to destroy the 456? I realise that’s not meant to be something we’re happy about, but it’s worse than just ambivalent… it might be dark edge too far, and we’ll just have to wait and see whether the character can survive it.

As for the series overall, it has been blessed by some great performances including Peter Capaldi as the grey man used as the Prime Minister’s plaything, Kai Owen as Rhys (the ‘heart’) and Susan Brown as Bridget Spears. And Eve Myles too – not a favourite of mine usually – really came into her own. It was, however, also quite unbalanced and maybe the final episode approached emotional overkill at times. But then, this is sci-fi, it aims to go one step beyond reality, and entertain. And I was very entertained.