Say what you like about Russell T Davies, but there are few writers in the UK who have shown anywhere near his capability for setting up a premise. More than once on Doctor Who, he’s written a terrific first part of a story (even if the corresponding concluding episode has rarely matched it), and the opening episode of Torchwood: Children Of Earth – his first for the show since the start of season one – does little to dilute his reputation.

His script kicks off with a short prologue in 1960s Scotland, which sees a busload of small kids walking towards a strange light. Before you can say Close Encounters, we’re back in modern day Wales, as Torchwood picks up from where the dramatic second season left off. The team are down to three, with Jack and Ianto now a ‘couple’ of sorts (that accounts for a good minute of dialogue in the episode), and yet the depleted group are about to face arguably their mightiest challenge to date.

But before we get there, Davies has fun setting things up. Ianto and Jack, for instance, we meet at a hospital, where they pull a strange creature out of the stomach of a dead man. This brings them to the attention of Dr Rupesh Patanjali. He seems more interested than most in Torchwood, and eventually follows the team back to the bay. There, Gwen decides she’s going to take the initiative and talk to him, as a possible new recruit.

Yet before we get that far, the main threat of the story has begun to emerge. Twice in one morning, all of the children of the Earth stop, arranged neatly around UK school times. If you can excuse the odd child who’s incapable of playing along with the game of musical statues, then it’s quite a sinister scene, and director Euros Lyn eats this kind of stuff up for breakfast. In fact, Lyn throughout the episode mixes his establishing shots, handheld and close-ups really well, and keeps things both exciting and interesting. Even when the events slow down in the middle of the episode as Jack and Ianto go off to their respective families to find a child, you’re always aware that the pace is ticking. But his mixing in of images of still children, who eventually start chanting, is arguably the most striking visual of the episode. That's even before we've had time to consider why they're all speaking English. Hmmm.

And yet more threats are converging. Inside the Home Office, Peter Capaldi as John Frobisher finds out about the children from Colonel Oduya (Charles Abomeli), and we get as a result some insight into the workings of the government (and the fact that Martha Jones is on her honeymoon). Keep an eye out too for Lois Hababa (Cush Jumbo), whose plot devices require the biggest leap of faith, though. We’re asked to believe that she can get into major secret information thanks to a handy Post-It note with a username and password attached to the screen, and thanks to this psychic-paper-alike device, she can access highly confidential information. It’d be more believable if the head of MI5 had personal details put on Facebook or something, and you hope it's a deliberate plot device rather than a bit of a cheat. Either way, Hababa – a so-called first day operative – has more going on that Davies is going to tell us about in episode one.

One such piece of info she discovers is the order from Frobisher (and Peter Capaldi really is excellent here), once the Prime Minister refuses to have his name involved on any level, to kill a collection of people, with the name of Jack Harkness at the bottom of it. Haven’t these people watched the first two seasons?

The other ingredient that Davies throws in is a man called Timothy, in his 50s, who joins in when the children freeze again and start chanting “We Are Coming”. He’s the only man on the planet to do so, and naturally, this gets people interested.

The chanting voice? Well this, as the aforementioned Frobisher discovers thanks to the helpful man who kept old equipment going in a back room (and shows with expensive science-fiction sets always need one of those), is the 456 talking, so named because of the frequency that they broadcast on. Said frequency has been dead for some time, but suddenly, it’s come back to life.

Ultimately, it’s when Torchwood starts investigating Timothy, and discovers that his real name is Clement McDonald, that the fit starts to hit the shan.

In a move straight out of a Bourne movie, the mere mention of his name is intercepted, and kicks off a chain reaction in the corridors of the powers that be. Thus, while Gwen interviews Clement, and discovers both that he was one of the children in the Scottish incident at the start of the show, and – after literally having a good sniff round – that she’s pregnant, the tempo moves up another notch.

This was good stuff to this point, I thought, and as is often with Davies, it’s the little details that he puts in his scripts that add a little depth. We learn, for instance, from Dr Patanjali, that bodies have been going missing from his Cardiff hospital (later exposed as a ruse to get Torchwood interested), and also that suicide rates have gone up since people became aware of the alien threats. We also get some nice moments, particularly with Captain Jack talking to his daughter, and Ianto sort-of coming out to his sister. None of these things matter necessarily in the greater scheme of things, but it does flesh out some of the characters and antics of the past couple of seasons, and points to some very real ramifications for all concerned.

The back end of the episode, to be fair, could have been transplanted out of numerous Doctor Who adventures. The children start chanting again, the shutters start coming down on Torchwood, and it’s clear that someone is coming after them, as well as there being a broader threat to the planet. Cue lots of loud music, a big explosion, and an hour’s worth of solid foundation laying coming to an end.

There’s clearly been money thrown at this shorter Torchwood run, although it seems like a modest amount has been spent on episode one. Yet that’s not a problem. Without showing us a single alien, or going over the top with a particular effect, it’s laid down enough questions, and delivered enough of interest, to get me tuning back in tomorrow at the same time.

And Davies, once more, has proven that he can deliver blockbuster opening episodes, even if they are reliant on a couple of trusted conventions. For he’s clearly an ideas man, and the intrigue generated by the premise, and this opening gambit, is something that’s going to be fun to see explored over the coming four nights. See you same time tomorrow, then...

• James Moran on writing Torchwood: Children Of Earth

Updated: thanks to the earlier posters who spotted the obvious thing I'd missed about the bomb in Jack's stomach. D'oh!