PLEASE NOTE: THIS REVIEW CONTAINS SPOILERS. OUR SPOILER-FREE REVIEW IS HERE.

The return of the Silurians is a logical choice for this current series of Doctor Who. For we’re in a run of the show where enemies have proper reasons for their actions, and given how comparably untapped the Silurians have been since the days of Jon Pertwee, they’re an interesting choice to bring back.

They’ve never been, and I see this as a fan of classic Who, the most sinister of monsters. But they’ve got a solid backstory, in that they were the residents of the Earth long before human beings came along ("they're earth-liens"). The Hungry Earth is respectful of that, and in bringing them to the fore of this episode, we get the first proper full-on person-in-a-suit monster of the series.

And in many senses, it’s a traditional monster tale, albeit with quite a dark edge. There’s a chase through a graveyard (interestingly with a child being chased), people being pulled underground, and the regular build up before the creatures themselves are revealed.

Writer Chris Chibnall, returning to Doctor Who for the first time since series three episode 42, is happy to take his time with all of this, too. And he’s right to: this is the first of a two-parter, and it feels very much in keeping with the classic structure of such stories. Thus, much of part one is establishing work, building up to the revelation of the depth and breadth of the foe the Doctor and his band are up against in the next episode.

That band this time round includes Amy and Rory once more (although Amy seemed more dressed for Rio, their supposed original destination, than Rory!), as well as some help from Dr Nasreen Chaudhry and Tony Mack (played by Meera Syal and Robert Pugh respectively). The pair are drillers, and very good ones at that. When we meet them, they’ve drilled further into the Earth’s crust than anyone else in history, but unwittingly, they’ve ignored the warning signs – the blue grass in the area – that’s suggesting they keep away.

Not that it appears to be a warning. In fact, the Welsh valley where the episode is set, ten years into the future, is calm, quiet, sedate and gentle. Save for the great big drilling machine in the middle of it, of course.

The first sign that things are going awry arrives in the pre-credits sequence, as a security card earns his dim points by sticking his arm into a fresh patch of earth that’s appeared. Down below he’s pulled, although given that we’ve met his wife and child by this point, there’s little doubt that we’ll be meeting him again.

By the time we do, Amy Pond too has been pulled underground, which serves to take her out of the bulk of this episode, and instead we spend a bit more time with Rory. There’s still a lot we don’t know about Rory, you can’t help but sense, but I’m getting more interested in his simmering distrust of the Doctor. By this time in their relationship with the Time Lord, most characters have warmed to some degree to his way of working. But I don’t get that vibe from Rory, and combined with the cantankerous way that Smith’s brilliant portrayal of the Doctor takes him, they’re hardly the best of friends ("you should have tried harder", Rory yells at the Doctor here).

I might be off the mark there, but I can’t help but feel something of real note is approaching where Rory is concerned. Could it have something to do with the supposed sighting of Amy and Rory ten years into the future, too? If that really was them waving from across the valley, aren’t they in danger of crossing their own time line? That’s what the Doctor, if you buy into some theories, has been doing throughout this series too. If that all comes to fruition, then all those cracks in time – and we don’t get one in this episode – are likely to increase in significance.

But back to the story. As Choudhry and her team drill down, it becomes clear that something is drilling up, and thanks to a lot of computer graphics on screens, we learn that whoever it is who’s coming to the surface won’t take too much longer. Cue the logical thing: peg it. Only they can’t peg it, because there’s quite a fancy CGI effect keeping them all prisoner in the vicinity.

And that CGI effect is used for good purpose when the episode begins to take its darker turn. Down go the lights, and Chibnall gradually ups the ante. We see a Silurian interrogated by the Doctor (a lovely scene: it’s terrific sometimes when Doctor Who opts for a good chat rather than a run around another corridor), and the explanation comes forward that they’re a generally peaceful race, until you disturb them (we also get said Silurian declaring that "one of you will kill me" to the episode's companions - could that be Rory?). The look on the Doctor’s face says it all: they’ve been antagonised, and it's all building up to the Silurian equivalent of Planet Of The Daleks, where the episode ends with the full scale of the Silurian threat exposed.

It combines to form a tidy, effective part one, one that didn’t overplay its hand, and inevitably saved its big moments for the episode to come. But it was entertaining nonetheless, channelling quite a lot of the feel of old Who, and doing it successfully enough.

We'll see how this all pans out in seven days' time with Cold Blood, then...

Our review of last week's episode, Amy's Choice, is here...