First broadcast 27 April 2013.

When the TARDIS gets caught in the grip of a deep space salvage trawler, it suffers tremendous damage – leaving the Doctor (Matt Smith) outside with a trio of salvage operators and Clara (Jenna Coleman) trapped inside within a labyrinth of tunnels, mysterious rooms and monsters. To save her life, the Doctor and his newfound companions must… journey to the centre of the TARDIS!

In a season largely dedicated to “blockbuster” episodes, styled as largely self-contained movies for television with an appropriately high concept, “Journey to the Centre of TARDIS” may just have the highest concept of the lot. The TARDIS has always been one of the most fascinating elements of the series, and “Journey” represents the first proper TARDIS-based episode since “Castrovalva” back in 1982. Notably, new series audiences had not seen much of the TARDIS bar one or two corridors, so an episode hunting around the heart of the machine makes for a wonderfully enticing premise.

I remember being concerned going into the episode the first time around that I was going to be disappointed. Writer Stephen Thompson was responsible for Season 6’s “The Curse of the Black Spot”, which seemed a deeply flawed episode. It was a tremendous relief to discover “Journey to the Centre of the TARDIS” was its exact opposite: smart, funny, well-paced, a little bit scary, brimming with strange ideas and liberally soaked in continuity references for long-term fans.

The episode’s guest cast – Ashley Walters, Mark Oliver and Jahvel Hall – are uniformly great. They mark the first guest cast of a Doctor Who to be entirely comprised of actors of colour – although you’d be forgiven for not noticing the fact, since they each play such distinctive and interesting characters.

After a brief respite in previous episode “Hide”, the series is back interrogating the mystery of Clara Oswald’s multiple incarnations through time. Here the Doctor directly challenges Clara to her confused face, which should have been an interesting development for their relationship. Instead time travelling shenanigans mean that, for Clara, the confrontation never occurred. We are, essentially, back to square one: the Doctor is perturbed, but nothing has actually developed in terms of plot. Doctor Who has always been rather lazy with its season-spanning arcs, which previous showrunner Russell T Davies relying on repeated catchphrases (“Bad Wolf”, “Torchwood”, et al) in lieu of substance. Here I feel Steven Moffat is even more frustrating: he throws in a superficial indication of an ongoing plot, but remove the fussy dialogue and scenes of Matt Smith looking frustrated, and it’s no better than writing “Bad Wolf” onto the set each week.

As I rewatch this season, it is becoming clear that such a weak arc is actually doing damage to Clara. There is no room to develop a rounded, interesting character, because time spent on her is time spent wiggling fingers at the audience and shouting “impossible girl” repeatedly. She honestly does not get a chance until Season 7 is out of the way and she can just be a normal person for a change.

Ignore the ongoing issues, and this is a fun, dramatic, high concept episode. It runs at a brisk pace, throws in some neat science fiction ideas, and – thanks to director Mat King – looks good while doing it.