LOTS OF SPOILERS AHEAD

Brilliant, brilliant, brilliant, brilliant, brilliant.

Appreciating that penultimate episodes are something that new Doctor Who/Torchwood is very good at, this was a meticulously jigsawed together escalation of the threat that’s been building for four days of Torchwood now. And it's leading into what looks like a cracker of a finale. Please, please, don’t blow it now, because Torchwood: Children Of Earth’s fourth episode has only been rivalled for me by the penultimate episode of Ashes To Ashes this year. A superb piece of television.

And before we go any further, let’s have a hearty round of applause for the cameo appearance by the voice of the Daleks himself, Nick Briggs, who was sitting proudly in the cabinet meeting. Marvellous stuff.

But down to business. The episode picks up from the superb cliffhanger at the end of last night’s instalment, but takes some time to explain it, rather than rushing through to get on with fresh material. We learn that Jack gave the 456 twelve children back in 1965, to stop them unleashing Indonesian Flu. We also learn here that the 456 have popped by before, back in 1918, with Spanish Flu wiping out 5% of the population in toe.

Moral of the story: the 456 are not to be messed with.

Via a formulaic perhaps but very effective mix of flashback and present day reactions, we then learn that Jack was pushed to be the delivery driver in a deal that swapped said twelve children in exchange for basically sparing the world.

Where all this material was at its best was in something simple, of course, namely the reaction in Clement’s eyes (although the “Come with Uncle Jack” line was really quite haunting). And while Clement went through his emotional responses in double quick time to allow him to become a useful part of the Torchwood crew without hating Jack too much in the end, you were left in little doubt just how much he despised what Jack did. You can hardly blame him, either.

The theory was, incidentally, that Clement survived the cut because he was on the cusp of adolescence. Second moral of the night: if aliens are landing, make sure you’ve got a bit of pubic hair.

Clement, at this point, does something entirely logical here, and shoots Jack dead. Only not dead, of course. But you get the idea. Yet that’s the advantage Torchwood has with an indestructible character – it allows other characters to not have to surrender to plot devices to keep them alive. For the record, Clement is also the first person in some time to aim a gun at someone and actually hit them in this show.

The episode then took a little time to plant a seed of Ianto’s disappointment in Jack hiding things from him. My notes as this was happening read ‘Could Ianto be a gonner then?’. We’ll deal with the answer to that shortly.

There were a few more moments of pieces being moved around the board before the episode suddenly accelerated. For instance, Jack’s daughter and grandson are now in custody, giving Alice the chance to warn moody military woman that “a man who can’t die has nothing to fear” (this wasn’t an episode where many characters minced their words, if you couldn’t guess).

Yet soon enough we were back to Thames House, as Frobisher went back to talk to the tank of smoke.

Thames House

The 456, we learn, are wise to the fact that someone is watching them, which Clement, back at Torchwood’s makeshift headquarters, takes to mean that they know he in particular is watching them through Lois’ immensely clever contact lenses (and to be fair, those contact lenses are a brilliant plot device, too). Frobisher, played again with consummate excellence by Peter Capaldi, lets slip that he’s in contact with the PM, and questions the 456 as to what they want to do with the kids. This is the episode’s cue to ratchet the tension up a good few notches. It happily obliges.

For the 456 invite what first looks like a Star Trek red shirt into the tank with his camera. My fear here was that the show was going to let the identity of its main villains out of the bag, but turns out I did Children Of Earth a massive disservice there. Because not for the first time, it pulls a genuine surprise.

At first, I’m sat there thinking that they’re doing some kind of Aliens knock off with a character I’ve not seen before and is thus doomed to die. And then? We get to see the genuinely creepy and chilling child, who, of course, turns out to be one of those taken in 1965.

It was a brilliant moment, and the show threw plenty of red herrings in there to distract you. Blood pressure monitors? Check. Shaky camerawork? Check. Alien tentacles and stuff? Yep, they were there too. But that mutated child figure? That was superbly done, and utterly effective. Mixing in just the right number of reaction shots, this was a moment with real impact, and a million times better than any monster of the week reveal could have managed.

In the midst of this, we also find out that the 456 have recorded Frobisher’s conversation earlier in the week, and thus the fit hits the shan back with the Prime Minister. The Brash American Man quickly realised that the UK has been hiding the 456 from the world before – it’s reinforced with a bit of rolling news coverage later on, in case we didn’t get the message – and all hell is about to break loose. Even Nick Briggs seemed powerless to stop it, and he can make Dalek noises for a living.

But this is when, in yet another moment of real measure, we cut back to a quiet, broken Jack. The varying of pace was very well handled, and Jack here knows he’s responsible for all of this in some way, and Ianto knows he’s hiding something. All those little exchanges between the pair over the past week really start to have a pay off here.

And as for John Barrowman? How good was he here? John: seriously. Cut all those shitty talent shows out and do more of this instead. Several times he’s been asked to put across emotions that feel crueller than if his character had been killed, and every time, he’s knocked it out of the park. I’ve always thought he’s better at playing Captain Jack in Torchwood than Doctor Who (not least because he's given more interesting things to do), and any hint of doubt over that was duly eradicated here.

Chills

He pulls himself together though and has another brittle conversation with Frobisher, and then the episode – which had been terrific to this point already – really shunted up a gear.

And it produced its most chilling scenes not with the aid of the special effects budget, but with good old fashioned quality writing. The moments around the cabinet table, as scarily plausible arguments were pitched as to how many children – or ‘units’ – should be sacrificed, were as gripping and horrific as anything we’d seen all week (and perhaps all year, too).

And they were so because they were all so reasonable. This wasn't two dimensional polticians groping for any old answer. They were under pressure, and coming up with horribly logical solutions. That was the scariest thing of all.

The 456 rejected the politicians’ counter offer fairly quickly in the end, and then we get another load of freaky chanting kids just in case we'd forgotten about them. After all, Children Of Earth had subtly, without us really noticing, put the anklebiters to one side for much of the episode, instead talking about them in dismissable terms. Here, though, the kids themselves were back, with different children in different countries chanting numbers that equate to 10% of the child population in each. Again, the chanting was far more effective than the voice of the 456 back at Thames House. Talking of which, said 456 were not taking no for an answer. And still, they were being kept in the shadows, with 80% of the series done.

There’s a lesson here for any aspiring sci-fi or horror writer. Take their silly voice away for a minute, and the 456 are a compelling threat because we know so little about them. There’s no big spaceship with a target on it here to eventually shoot down. No 'take me to your leader' moment. There’s no little creature to fire at. It’s a threat that humanity has no idea of the scale of, and there’s no obvious physical manifestation of it. It’s like counting the shadows again.

Once we get through the authority figures making lots of statements querying how to sell the sacrifice of children to voters, and considering the “socially useful” benefits, the character of Lois finally steps up. Thus far, her main use has been to wear contact lenses, but here, she delivers the Torchwood threat. No matter that the authorities now have Jack, Ianto and Gwen in their sights, Torchwood has them all recorded, talking brazenly about human sacrifice (and revealing the real reason for school league tables, too...). It’s great that the episode basically stopped for ten minutes to build all this material up, allowing the Torchwood team to use it as legitimate and believable currency.

Farewell

And then we get to that quite brilliant ending. Captain Jack has, understandably, had enough by this point, and confronts the 456’s tank. It’s a smashing face off, too, that kicks off when Jack declares, “I’m here to explain why this time you’re not getting what you want.” And then? A reasoned, yet sinister, argument back, quoting child mortality statistics. There’s no softly-softly two dimensional posturing here. Hard facts, and not easy ones to swallow, are thrown back in humanity’s face.

This, however, all leads to tragic consequences when Jack refuses, in spite of past matters, to yield again to the 456, effectively declaring war. They don’t take this well, leading to Clement’s death back at Torchwood (and I wonder if any of the children of the world have faced a similar fate, too?). And they then hit Jack where it hurts the most, releasing a poison that ultimately kills Ianto.

Say what you like about Torchwood: it doesn’t half take some risks. It knocked off two major characters at the end of season two, and here it robs the show of another, who for many was the star of the programme. It’s shocking, brilliantly handled, and the distraught reaction from Jack told its own story. For all the posturing, the man can be hurt, and hurt badly. And in the world of Torchwood? It seems there's only one character, no matter how established, who's ultimately safe. Everything else is up for grabs.

The final scene where Gwen and Jack sit amongst the room full of corpses was melancholy, still, and yet devastating. And it left you kind of hoping that there was another week of this to go, and not just one more episode.

Tomorrow? It all, sadly, comes to an end, and I’m passing the review mantle over to Cameron, who’ll be writing up his thoughts once the credits roll.

For now? That was, and I don’t think I’m underselling it, a stunning piece of television, that not only stakes its claim as Torchwood’s finest hour, but leaves the overwhelming majority of new Doctor Who episodes in its wake too. Bring on the finale....

• Episode 1 review
• Episode 2 review
• Episode 3 review