Doctor Who: The Halloween Apocalypse’s 12 biggest questions

We try our best to answer all these burning questions – and more – and ask a few more of our own in response to The Halloween Apocalypse. Starting with…

What caused the Flux?

It's "the end of the universe" – but what exactly is the Flux? What's causing it? Is this "spacial anomaly" a natural phenomenon – something like The Big Crunch (a hypothetical scenario for the ultimate fate of existence, in which the universe – which has been expanding since the Big Bang – eventually starts to contract and collapses in on itself)?

Or is it man-made? Certainly the climax of The Halloween Apocalypse, in which the Flux is seen to change course (“The end of the universe is chasing us!”) seems to suggest it might be being controlled by some outside force...

But if it is the work of a specific group or individual, who? Is Swarm responsible? It's possible – though from what we glean from Karvanista, it would seem the Flux has been underway for quite some time, certainly before Swarm was freed from his containment chamber. Then again, we actually witness Swarm's escape inside the Doctor's mind... so who's to say how long ago it actually occurred?

Erm... maybe it's the Master? Never rule that guy out when there's trouble afoot.

Who is Swarm?

New (or should that be old?) baddie Swarm (Sam Spruell) claims to be an ancient enemy of the Doctor, who battled her across space and time many years before. The only problem? The Doctor’s missing her memories of that period in her life, giving him the upper hand in their new conflict.

It’s currently unclear what species Swarm is or what his plans are, but we do know he has a sister/sidekick called Azure (Rochenda Sandall), a handy trick for disintegrating his enemies and an ability to “renew” himself in some way. Oh, and he’s also been in space jail since the Dawn of the Universe, watched over by the Time Lord black ops organisation The Division.

Still, largely he’s still a bit of a mystery – though we may have one theory for what his connection is to the Doctor…

What is the Division?

Right yes, some background. In series 12 (specifically the episodes Fugitive of the Judoon and The Timeless Children) we learned that the Doctor’s race the Time Lords used to have a kind of secret police force, who didn’t officially exist but travelled round the universe getting involved in opposition to Gallifrey’s strict non-interventionist policy.

We don’t know too much about The Division other than that they have snazzy crystal guns, strange uniforms and – crucially – that the Doctor used to work for them, before having her memories wiped and regeneration cycle reset. Now, she appears to be looking for them starting with Karvanista (Craige Els), one of their former operatives, in order to find out what happened to her memories.

And she might be getting closer – in this episode we see two more Division operatives guarding Swarm before he escapes, suggesting there are still quite a few of them knocking about the universe for the Doctor to find.

What is going on with the tunnels in Liverpool?

In what quickly becomes The Halloween Apocalypse's stock-in-trade, the episode zips from the Doctor and Yaz's high-octane escape from an acid ocean back to Liverpool, 1820, where one Joseph Williamson (Steve Oram) is digging a series of tunnels beneath the city.

Though he won't be drawn on the purpose of his tunnels, Williamson warns that something "lies ahead" and that "the cataclysmic, the impossible" is coming for us all. Then we time-travel 201 years into the future and nothing more is seen of this sub-plot for the remainder of episode, bar a brief glimpse of a moody-looking Williamson in the closing montage.

So what's going on here? Well, presumably all will be explained in one of the remaining five episodes of Flux – but what makes this thread especially interesting is that Williamson is a real historical figure, who is indeed best known for having a series of tunnels constructed in the in the Edge Hill area of Liverpool. The tunnels were built over a 30-year-period, between 1810 and 1840.

The purpose of these extensive subterranean excavations remains a real-life mystery – Williamson was said to have kept his motives behind building them a secret, leading to much contemporary speculation as to their purpose, with popular suggestions being they were being used for commercial quarrying, that they were built purely as an excuse for philanthropist Williamson to employ the poor, or that they were simply the purposeless folly of an eccentric man.

We expect Doctor Who's own explanation will prove to be rather more interesting...

Read more about Doctor Who:

• Doctor Who - The Halloween Apocalypse review: Chris Chibnall turns up the heat for a fast, fun-packed opener
• Doctor Who’s The Halloween Apocalypse is like a series finale, but backwards
• Doctor Who's series 13 premiere featured nods to an old Doctor and two classic companions

What’s wrong with the TARDIS?

A strange little subplot in The Halloween Apocalypse is the malfunctioning TARDIS, first presented when one of the crystal columns starts leaking an oily, black substance that clearly unsettles the Doctor (though she tries to cover it up).

Later, the TARDIS keeps stalling when they try to travel, and moving the door to different parts of the control room for no apparent reason (which also weakens the defences when the Flux rolls in later on).

So what’s going on? It could be that the presence of the Flux was in some way interfering with the TARDIS, or that the release of Swarm led to it malfunctioning (it started going wrong around the time he contacted the Doctor mentally, and she does have a connection to the TARDIS).

Or it could be that some other threat is messing with the Doctor’s ride. Watch this space…

Did the heart of the TARDIS do… anything?

Speaking of the TARDIS – in the episode’s final moments the Doctor pulls of a kind of Hail Mary, opening the TARDIS console to pour the energy of the time vortex into the Flux. Unfortunately, what it does is “not much apparently” and the Flux hits the Doctor, Yaz and Dan anyway, leading to the episode’s ending.

It’s an odd, slightly anti-climactic moment if the Doctor’s little trick truly didn’t have any effect, so we’re wondering whether this will pay off in next week’s episode. Maybe, this is how the Doctor and co. end up zapped back in time to the Crimean War with the Sontarans – or maybe it’s even what makes the Flux even more dangerous.

Who is Vinder?

The Halloween Apocalypse provides us with a relatively brief glimpse of the much-vaunted Vinder – Jacob Anderson's character appears to be Doctor Who's equivalent of Thunderbirds' John Tracy, stuck with the thankless role of being stranded in outer space on an observation post where there's precious little to observe.

Vinder's been described by Anderson as a "man of honour" but thus far we know precious little else about him – how did this "very good fighter pilot" (again, Anderson's words) end up stationed on Observation Outpost Rose? It's clear that there's no love lost between Vinder and his employers, so perhaps he refused an order that went against his moral code and was given this ignominious posting as a punishment?

And what exactly was Vinder supposed to be monitoring? Was it the Flux, or something else (he seems startled by the sudden arrival of said destructive phenomenon, which suggests the latter)? Is it even important? How will he survive getting gobbled up by the Flux? And given that the next episode of Flux, War of the Sontarans, seems to be taking us on a trip back to 1850s Earth and the Crimean War, how long will it be before Vinder crosses paths with the Doctor and the rest of Team TARDIS?

Is "Observation Outpost Rose" more than a coincidence?

Speaking of "Observation Outpost Rose", is it purely a coincidence that Vinder's base of operations shares its name with one of Doctor Who's most beloved companions? It might very well be, but you'd think Chris Chibnall would be aware that you can't throw the name "Rose" into the mix, even in this off-hand manner, and not expect fans' tongues to start wagging.

Now we're not seriously suggesting that Billie Piper is going to appear in Flux – though she did suggest fairly recently that she'd return to Doctor Who "if the circumstances and the story were right" – but could there be some link here to her character? Perhaps there's some time trickery involved and we'll see the Doctor visit a point in history prior to where we first meet Vinder, with the Time Lord christening the newly-built Observation Output and naming it after an old friend?

Or maybe it's totally unrelated. What's in a name, after all? That which we call Observation Outpost Rose by any other name would smell as sweet...

Why are the Weeping Angels hunting Claire?

In a little tease for a future episode, we meet Annabel Scholey’s character Claire, who says she knows the Doctor and Yaz from their future and promises to see them again at a later time. However, shortly after leaving the duo behind she’s stalked by a Weeping Angel, who after a tense scene manages to perform its party trick and zap her into the past.

It’s an intriguing sequence, because it seems like Claire has met the angels before – she knows to keep her eyes on them at all times, and her comments to the Doctor and Yaz that she’s taking “the long way” back suggesst that she might already have been sent into history, forced to live through it to catch up with her own time period.

So why do the Weeping Angels have such a grudge against her? We know Scholey will turn up in future episodes, so we’re guessing that we’ll see exactly how she met the Doctor and incurred the Angels’ wrath soon (our prediction is episode four).

Presumably, though, we’ll also need to catch up with this version of Claire to resolve her story, which is confusing. Worth remembering that the original Weeping Angels episode was the one to introduce us to the concept of wibbly-wobbly, timey-wimey stuff…

Is Dan hiding some kind of secret?

We might be overthinking this, but there’s a moment in The Halloween Apocalypse just before Dan (John Bishop) is kidnapped by Karvanista when the Lupari warrior tries to use telepathic suggestion on his captive.

But it doesn’t work on Dan, which seems to surprise Karvanista. Is this some sort of suggestion that Dan has hidden depths or abilities, or just a case of bad tech? We might have to wait and see…

What does Azure want with Diane?

On a similar note, we have to wonder whether Dan’s sort-of squeeze Diane (Nadia Albina) has some hidden purpose, given that she’s abducted by Azure (Swarm’s sister) towards the end of the episode to splash around in the Upside-Down (or whatever its BBC equivalent is).

Is this just an attempt to manipulate Dan, and thus the Doctor? But how would Swarm and Azure even know about Dan, let alone his connection to Diane? Sometimes, it feels like we’re adding more questions than answers here.

Why is there a mattress on the floor of the TARDIS?

Erm... look. Maybe the Doctor is such a genius-level intellect that she had planned her and Yaz's escape from Karvanista in utterly meticulous detail, right down to the perfectly-positioned mattress lying on the floor of the TARDIS – ready to broke their fall as they were propelled through the doors and onto the console room floor.

Or maybe the Doctor and Yaz got lucky – steady on – and the mattress just happened to be lying around after some previous misadventure?

Still, you can't help but think the "Thasmin" shippers are going to have a field day with this one...

• Doctor Who’s Mandip Gill addresses Yaz/Doctor romance rumours: “That’s what happens to people naturally”

Doctor Who: Flux continues on BBC One on Sundays. For more, check out our dedicated Sci-Fi page or our full TV Guide.