Flatline sees Doctor Who returning to Earth, and to the present day. It also proves another interesting slight tonal shift for the series, and offers further evidence for series 8 being the most consistent and entertaining run of Doctor Who in some time.

The back third in particular of this one is great. Given that we're in spoiler-free territory on this one, there's not actually anything of note that we can give away (nor would we want to). But if you're fed up of watching films and TV episodes that come up with an interesting idea and don't manage to get it to build to anything, then worry not where Flatline is concerned. This one delivers.

And it's an episode bursting with some interesting ideas. Writer Jamie Mathieson made his Doctor Who debut last week with Mummy On The Orient Express, and for Flatline, he keeps a mystery element working through the core of the episode again. But he also ties it to some good ideas that he gives himself the space to explore and realise.

At first, in truth, we weren't entirely convinced that the central narrative was quite going to work. It seemed a fine idea in itself, but nothing that would lift the story into something more than that. Yet Mathieson develops it, and adds in ingredients that really do impress, and impress heavily.

Furthermore, realising one or two of those ingredients relies heavily on the special effects team delivering something that looks really quite different and effective as the episode progresses. Again, at first, you may not be sure they've quite pulled it off. By the end, it's some very tasty drinks all round. It's rare that CG work can be as unnerving as it is in this particular Doctor Who, and huge credit should be awarded.

Flatline also plays heavily on the relationship and roles of both the Doctor and Clara, in a way that ties in to a lot of what's been going on throughout Doctor Who series 8. It also continues the horror themes and undertones that we've been seeing throughout, this time with returning director Douglas Mackinnon having fun with dark shadows and creepy creatures. Not for the first time in recent weeks, there's something really quite unsettling about this one.

Furthermore, Flatline is an episode of Doctor Who that has answers to both the questions 'what's it about?' and 'what it really about?'. If you're looking for a mildly close recent parallel, then it could be very, very loosely tied in that sense to the excellent series four episode, Turn Left. But to be clear: it doesn't overlap too much with that one at all, rather that the ethos behind it bears a similarity.

It also leaves things, not for the first time, interestingly positioned, as Doctor Who series 8 heads - already! - towards its final three episodes. Can the standard be kept up until the end? The signs are certainly positive, and Flatline does not let the side down at all.

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