Doctor Who: The Power of Three – series 33, episode four

This week's alien-invasion story offered plenty of nostalgic thrills and comedy as well as a tender moment between Amy and the doctor

'Tender dynamic': Karen Gillan as Amy Pond and Matt Smith as the Doctor in The Power of Three. Photograph: Adrian Rogers/BBC

SPOILER ALERT: This weekly blog is for those who have been watching the new series of Doctor Who. Don't read ahead if you haven't seen episode four – The Power of Three

Dan Martin's episode three blog

'Civilisation saved, surfaces wiped. What more could any woman ask for?'

Not beating about any bushes, I bloody loved this episode. You wouldn't want the show to be like this every week any more, but here was a nostalgic run through the all the best bits of the Russell T Davies era. We got a modern-day Earth-invasion story, complete with a comedy parent, a truckload of continuity nods, and newsreel cameos from Professor Brian Cox and Lord Sugar. Yes, it also had the weaknesses of some RTD adventures – the ending was so underdeveloped that even a magic button couldn't explain it – but The Power of Three was, in every sense, completely gorgeous; RTD spiked through with the swagger that is the hallmark of the Steven Moffat series.

Back in their geographically non-specific hipster hamlet, the Ponds are continuing to get away with murder. Amy's insecurities over the functionality of her uterus have melted away like so much lazy exposition, and having sashayed on from her modelling career, she now makes a living – in the current journalistic climate – writing travel articles for magazines. Rory, meanwhile, has developed a sweet deal with the NHS where he can swan in and out of employment to go off with his time-travelling mate to the Day of the Dead festival, or to spend his wedding anniversary at the Savoy in 1890. And of course, they both cheerily neglect their friends.

Much as I love them on-screen, Amy and Rory would be incredibly annoying people to actually know. And yet The Power of Three, both a celebration of the Ponds and a thoughtful piece on the nature of growing up, is unashamedly heartwarming from start to finish. The slow invasion of the Shakri presents the first attempt on Earth since the Silence in Day Of The Moon, and even that's moot since they've possibly been here all along. And with that comes the return of UNIT, the military's extra-terrestrial division. Were this episode not enough of a fangasm, Jemma Redgrave's steely UNIT leader Kate turns out to be the daughter of the legendary Brigadier. Amazing!

'I'm not running away from things, I'm running to them, before they flare and fade for ever'

Moffat has said of the big Amy/Doctor scene – in which the two of them sat outside the Tower Of London, contemplating – that it's the moment that sums everything up, and that he's only sorry that he didn't write it himself. Chris Chibnall, whose Who stories so far haven't exactly been noted for their memorable characters, completely nailed the lovely dynamic between The Girl Who Waited and her Raggedy Doctor. Matt Smith and Karen Gillan made the most of their chance to wallow for a final time in the pair's tender dynamic – and the most unusual Doctor/companion relationship in the show's history.

Pond watch

We've heard no mention of Amy's parents since Augustus Pond was spotted in passing at the wedding in the rebooted universe. And that itself may turn out to be significant next week (as might the duck pond in Leadworth), but Brian Williams is easily the best companion parent since Jackie Tyler. What a lovely, brave, brilliant man. And, in fact, it's him that urges Amy and Rory to go back out travelling through time and space. But now the pair have accepted they can can maintain both lives after all, we can probably discount lack of interest as the reason for their departure. So what else could possibly go wrong?

Fear factor

Turns out there really is something incredibly sinister about small black cubes. And when they all came to life en masse, we got a behind-the-sofa moment from the most unexpected source.

Mysteries and questions

Below the line, there has been a view that the references to Christmas each week are significant – and this time we saw Christmas actually happen, albeit on a hospital ward. Could this be important for Amy and Rory's endgame – or foreshadowing the fact that the Doctor will meet his new friend at Christmas?

@Bluesqueakpip makes the excellent point that the Jenna Being In Every Episode Theory could indeed still have legs because the previous two episodes had female-voiced computers. Could Oswin/Clara be trying to get some sort of message out to the Doctor across time? (However, after three viewings, I couldn't spot one in this episode.)

@JimTheFish and @Juniperfish have been wondering whether this darkening Doctor could be the Ganger one from last year, but I didn't think there was much to support that this week. And a lot of you seem to be reading something into the fact that the barmaid from last week looked a bit like Alex Kingston. Really?

Time-space debris

• In a scene that was unfortunately cut, Amy and Rory contemplated getting the Doctor a babysitter.

• Chris Chibnall has certainly done his homework. Kate Lethbridge-Stewart, the Brigadier's daughter by his first wife, Fiona (we met his second, Doris, in 1989's Battlefield) appeared in 1995 direct-to-video UNIT spin-off Downtime and its sequel Dæmos Rising, where she was played by Beverley Cressman.

• The Doctor invented yorkshire pudding. Well of course he did.

• Steven Berkoff!

• Does the off-screen appearance of a Zygon count as a canonical appearance from David Tennant's favourite monster? If so this would be only their second appearance, after 1975's Terror Of The Zygons.

• The Doctor's withering dismissal of "Twitter" is not unlike Matt Smith's own attitude to the social network of doom.

• "If Fred Perry could see me now, eh? He'd probably ask for his shorts back."