Though it's been an iconic fixture of his adventures since the very first episode in 1963, very few Doctor Who stories have taken the time to explore just what the TARDIS is and what it can do. We know that it can travel through time and space. We know that it's a sentient machine which can reconfigure its interior at a molecular level, and that it's supposed to be able to change its outward appearance to blend in with wherever and whenever it lands, but the chameleon function got stuck as an old British police box and the Doctor never bothered to fix it. We also know that it doesn't like Clara.
Beyond those basic facts, the TARDIS remains a mystery. And it remains a mystery after this rather aimless and garbled exercise in corridor running, which offers a few fun nods to Who history but fails to tell us much of value about the characters or the TARDIS itself.
The action starts with the Doctor offering to give Clara the chance to pilot the TARDIS as a way of making his vessel warm up to his new travelling companion. This involves putting the TARDIS in “basic mode”, which means that the shields which would protect it from attack are lowered. This coincides with the TARDIS crossing the path of a trio of grungy space salvagers, who use an illegal magnetic retrieval system to snatch it from its flight path. This almost tears the TARDIS apart, and results in the Doctor somehow ending up outside of the TARDIS while Clara is trapped inside. There's a leak, and the Doctor blackmails the salvagers – the bickering Van Baalen brothers, led by British rapper turned actor Ashley Walters, and their android assistant Tricky – into joining him on an expedition into the TARDIS to find Clara before its too late.
It's an inelegant opening and it establishes a sloppy tone that the episode never shakes. There's just too much that doesn't make sense, from the Doctor inexplicably making the TARDIS so cripplingly vulnerable without a second thought, to the mysterious way he ends up outside rather than inside, to the very concept of the Doctor requiring the help of the salvagers in the first place. They don't know anything about the TARDIS, an infinite ship, so the notion that three extra bodies will make the search easier is laughable.
From there, the episode basically spins its wheels with Clara running around corridors being chased by a charred humanoid creature that looks like it took a wrong turn on the way to Silent Hill, while the Doctor spends most of his time trying to stop the Van Baalen's from dismantling the TARDIS from within, thus making it angry. Here's a suggestion: maybe don't invite avaricious salvage men onto your ship by promising them salvage beyond their wildest dreams then act horrified when they start ripping the place apart?
It's stupid, but more galling is the way the episode doesn't even use its contrived set up to deliver any meaningful forward momentum to the Clara story arc. She discovers a vast library in amongst the TARDIS' many rooms, and a book that tells the history of the Time War. In there she learns the Doctor's real name, but little else. The notion that the TARDIS doesn't like or trust her is utterly unexplored even when she's alone in its most secret places and, once again, the question of her appearing and dying in different times is brought up and then dropped without any meaningful development. This plotline is really wearing thin now, with the Doctor appearing far more fascinated by it than the viewer.
Also marking time is the Doctor's story with the Van Baalens. There's a revelation about their android that is both completely obvious and entirely meaningless, a trite twist apparently thrown in there so that there's someone who can come away from this adventure having learned a moral lesson, no matter how shallow. Maybe if the Van Baalens had more depth, or if they hadn't cast the scowlingly wooden Walters, it could have worked. As it is, their ending feels pointless and unearned.
The resolution to the episode is no stronger than the opening, as it's revealed that there's a localised time leak somewhere in the TARDIS causing recent history to echo and repeat. The shambling creatures are the burned remains of Clara and the Van Baalens, from a possible future where they die inside the heart of the TARDIS, the Eye of Harmony, a dying star held in stasis by Time Lord technology. That's a pretty powerful idea – being stalked by your own chargrilled corpse – but the episode doesn't use it for anything more than basic running around and screaming.
In the end, the Doctor fixes the problem using the cheapest trick in the time travel story handbook: doing something in the past that means the future never happens and erasing everything we just witnessed. There's literally a magic button that, somehow, changes everything – even Bill and Ted had a more nuanced relationship with cause and effect than this clumsy narrative fudge. For a story that made so little progress in the first place, wiping even that little step forwards is unforgivable.
There are couple of notable moments. Audio from previous episodes dating back to The Unearthly Child can be heard as the TARDIS breaks apart. There are visual reminders as well, such as Queen Victoria's telescope from the second season episode, Tooth and Claw, glimpsed among the TARDIS' many rooms. A smarter script might have taken those strands and woven them into a story that was worthy of its premise but, those cute references aside, Journey to the Centre of the TARDIS is the worst kind of filler episode, one that offers up a potentially rich scenario but then leaves all the best questions maddeningly unaddressed. Compared to the wonderful Neil Gaiman episode, The Doctor's Wife, this one barely scratched the blue paint on the surface of the TARDIS and its relationship with those who travel inside her.