What is The Flux in ‘Doctor Who?’

For its big 60th anniversary celebrations, Doctor Who has turned the clock by, ooh, 13 years to reunite David Tennant and Catherine Tate as the (Fourteenth) Doctor and Donna Noble.

And yet while the first of the trilogy of anniversary specials was very much a love letter to the original Tennant era, the second dares to reference much more recent events in Whoniverse canon, even if fans would rather forget said events ever happened. Or else they actually have forgotten they ever happened.

In special 2, titled “Wild Blue Yonder,” an incorporeal creature from the edge of the universe that’s taken Donna’s form (it’s Doctor Who, just roll with it) taunts the Doctor over something called “The Flux.” Fourteen admits that he feels guilty over half the universe getting destroyed, which he believes is all his fault.

But, wait, hold up — half the universe got destroyed? What the flux is going on?

The plot of Doctor Who: Flux, explained

The Flux was the key concept in the 13th season of Doctor Who, a six-part miniseries airing in 2021 that went by the subtitle Flux. In it, Jodie Whittaker’s Thirteenth Doctor and her friends Yaz and Dan were confronted with a mysterious destructive force spreading across the universe, the titular Flux.

Across the miniseries, the Doctor discovered that The Flux was really an all-consuming wave of anti-matter originating from beyond the universe, which unraveled every particle it touched. Its origins, it turned out, were intrinsically tied to the Time Lord’s own. The creators of The Flux were revealed to be Division, a shadowy espionage organization — kind of a Gallifreyan CIA — that the Doctor had once worked for centuries ago, and had only just regained her memories of. Run by the Doctor’s adoptive mother figure, Tecteun, The Flux was essentially done as an act of revenge, to kill the Doctor and destroy everything she cared about.

In this way, the Doctor would naturally feel some guilt for the destruction The Flux caused. Especially as, in contrast to the usual way Doctor Who stories work, the universe stayed half-destroyed by the end of the season. In the Flux finale, the Doctor did prevent a second Flux wave that would’ve finished off the rest of the universe, though, so they didn’t do too shabbily.

Nevertheless, the memory of The Flux is apparently still haunting the Doctor, even if most fans had completely forgotten this (admittedly little-loved) season was even a thing.