‘I’m going to pull time apart for you.’ Frustratingly, this one belonged in the first half of the series when its lesson – that you can’t have your cake and eat it; that for the young woman to escape the old must be sacrificed – could have foreshadowed the fate that would befall River Song if the Doctor saved Melody Pond. In fact, it seems like such an obvious parallel that I’m amazed no-one comments on it in the episode. Surely the whole reason this episode exists is to explain the Ponds’ inexplicable indifference to their baby’s fate.

You can imagine a version of Let’s Kill Hitler where River, like the older Amy here, pleads for her right to life, while her parents balance unwriting their grown-up daughter’s existence to save their baby. And because they’ve already had to face this choice, perhaps making a different decision the second time around. That might actually have been a compelling “arc” moment with some genuine emotional pay-off. So why shove this to the back half of the series and not make the most of (presumably) the purpose of commissioning it? This is a much more vexing mystery, to me, than how the Doctor’s going to escape his fate at Lake Silencio. Or – and this is horribly plausible – it was all just a coincidence and no-one in the production team was paying enough attention to notice.

Looking past this baffling mystery, and the painful contrivance of the red waterfall / green anchor timelines, this is very good. It’s a triumph for Karen Gillan, given her best material and seizing it. Older Amy is tangibly a different character, rarely making eye contact because she’s been so long without human company and has lived at her wits’ end for 36 years. I particularly like what the episode says about her relationship with Rory,. There’s a heart-breaking moment when she picks up a long un-needed tube of lipstick, a moment of vanity as, even after decades, she wants to look beautiful for her husband. Her final, desperate run towards the TARDIS as the Doctor slams its door in her face, and her last conversation with Rory are tremendous.

Around it, there’s a slight sense that it’s a cheaper episode (the location interiors don’t quite sell the alien planet), but the design of the handbots and the austere aesthetic are strong, and Imelda Staunton adds a bit of star power, even if she’s only a disembodied voice (there’s a trend of this in the Matt Smith years – we’ve already had Michael Sheen, and Sir Ian McKellen will be along for The Snowmen). So, despite my reservation on the set-up, I like the execution. But they really wasted the wider implications for the Series Six story.

Dr Who will return in The God Complex

Next Time: The Blood Line