If War of the Sontarans was the most ‘traditional Who’ instalment of Flux, then Once, Upon Time is its opposite. While it delves into the vaster, more mythic elements of Chris Chibnall’s additions to the Doctor Who canon, this third chapter uses a convoluted, timey-wimey narrative structure perhaps inspired by Chibnall’s predecessor Steven Moffat.

Opening with the Doctor saving Yaz and Vinder from the deadly time storm by – what else? – pushing herself and Dan into it too, the episode then splits off into four main strands, as each of these lead characters is thrown into another point in their own lifetime.

The most important of these four strands – and the best – is the Doctor’s. Chibnall plays a clever twist here, as what initially seems to be the Doctor’s near future, with her and her companions taking the Temple of Atropos back from the villains who captured it in the previous episode, is in fact far back in her past. A particularly nice detail is that blue coat she’s wearing – not a new costume she picks up during this adventure, but a hint that she’s in the memories of Jo Martin’s ‘Fugitive’ Doctor. (At least, we were misled like this; if you sussed it was her past from the start, then well done, give yourself a biscuit.)

This trip into the Doctor’s hidden history sheds some light on her work for the Division, as set up in Series 12. Tying the new villains to this story arc is a great way to set up Swarm and Azure as serious threats – new to us and to Whittaker’s Doctor, but with a considerable past rivalry to be discovered by both. It’s also fun to see Martin return as the past Doctor (even if it’s pretty obvious the crew had her for about an hour in front of a greenscreen – but the series was filmed during a pandemic, so we’ll forgive that).

Once, Upon Time cuts between this memory and those of the Doctor’s three friends, with the characters wrongly appearing in each other’s memories as time falls apart – an exciting set-up that, to start with, gives a thrilling pace to the episode. But it soon becomes clear that the other three characters’ trips into their timelines don’t have quite the same narrative purpose as the Doctor’s.

Yaz’s scenes, rather than finding an interesting point in her timeline or giving her anything particularly useful to do, become mainly about setting up the Weeping Angels – the villains of the next episode. That said, the scene in which an Angel comes out of a video game is a great encounter in itself, a very Doctor Who crossing of the horrifying with the ordinary. The whole “an image of an Angel becomes itself an Angel” thing may have been one of the sillier additions Steven Moffat made to the monsters’ lore, but if you’re going to return to it, this is a hell of a way to do so.

(On a side note, a writing tip: please research what people call video games before writing lines like “nobody calls them video games.”)

Dan’s subplot starts off promisingly, using the collapsing timeline as a backdrop for telling us more about his past and his maybe-romantic-maybe-friends relationship with Diane, but Chibnall soon runs out of story to tell here, and instead Dan gets thrown into a random series of scenes, including the episode’s token appearance from Steve Oram in sideburns, and that part of his personal timeline where he just sort of stood around on Liverpool Docks.

Meanwhile, the time storm throwing everyone into bits of their past very conveniently picks for Vinder, the character we know least about, the moments that best explain his backstory. Thanks, time storm. Though Jacob Anderson’s performance is endearing, it’s hard to be entertained by this rather generic backstory – a hotshot pilot who won’t follow the rules, eh? We’ve heard that one before. The visiting ambassadors – a return to the annoying Chibnall-era trope of aliens who look exactly like humans – look suitably bored.

There is one more strand to the episode – the story of Bel, Vinder’s star-crossed lover. Though this additional subplot further convolutes an already convoluted episode, it does give us some of Once, Upon Time’s best scenes. We get to see the effects the Flux has had on the universe at large, with the glimpses of a major war between the Daleks, Cybermen and Sontarans, all fighting over what remains of the universe; this backdrop of vast devastation and chaos is helpful context to bolster the threat level of what we’re seeing in the main story.

And, like Yaz’s go at playing Weeping Angel Call of Duty, Bel’s confrontation with the Cybermen is a great little encounter, particularly the dying Cyber who coldly dismisses her statement of “love” as her mission. It’s a striking interchange of dialogue that efficiently gets to the heart of these cyborg villains (and almost makes up for last series’ embarrassing CyberMasters).

Back to the Doctor, who tidies all this mess by negotiating with the Mouri to get time fixed back up. Who exactly the Mouri are is intriguing – are they creations of the Time Lords, or the Division? Or a species native to Time enslaved by the Division, perhaps? It’s all fun to ponder, and we hope our questions are answered satisfyingly.

However, there is a sense in these scenes that Chibnall’s scripts don’t have a handle on how much we’re already meant to know; the Doctor speaks to the Mouri as if she already understands who they are, and then acts as if the Atropos section of Flux is all over with, which makes us worried that we won’t be getting any more explanation (writing tip #2: ambiguity within a story can be good, but be clear on what’s meant to be ambiguous and what viewers are meant to have picked up already).

So, a lot’s been set up, and a lot depends on how well everything is paid off. We’re certainly building up to something big, and the Doctor’s increasing bossiness towards her companions towards the end of this episode hints at some interesting shifts in the dynamic to come – again, fingers crossed for some satisfying pay-off.

Once, Upon Time may be a messy and flawed episode, but we were rarely bored ­– the pacing of it, the unusual narrative structure, the expansion on the Doctor’s past, and the brief but brilliant appearances from Cybermen, Daleks and Angels all work to keep excitement levels up. It’s great to see Doctor Who being this bold. This was 50 minutes of utterly chaotic TV, but compared to the mundanity that characterised much of the Thirteenth Doctor’s earlier years – and which only briefly bled into this episode when it came to Vinder’s story – we’re revelling in the chaos.