Doctor Who series 13 clue could point to the return of another classic villain

This theory comes from a hint dropped by Chibnall during a San Diego Comic-Con panel, when he and the cast were asked to describe the upcoming series 13 (aka Doctor Who: Flux) in one word. Rather than go down the usual path of muttering “epic” or “exciting” Chibnall instead went for “Swarm,” leading to a frenzy of speculation as many (including us) tried to decipher whether Swarm referred to a classic monster, some new organisation or something else entirely.

But now, fans think they’ve cracked what Chibnall was saying based on the new series 13 teaser – because if you lay out the confirmed monsters appearing in Flux, they perfectly match the teaser word’s initials. Or, to lay it out more clearly…

S – Sontarans

W – Weeping

A – Angels

R – Ravagers

M –???

In other words, it could be that Chibnall’s use of that word was a clever nod to the threats the Doctor would face over the course of the series, or even some kind of group designation used by the monsters in the series itself (though it is hard to imagine the Weeping Angels really getting into acronyms).

The kicker? That mysterious missing M, which could point to none other than one of the Doctor’s greatest foes – rogue Time Lord the Master, as played by Sacha Dhawan in recent appearances. While not yet confirmed for series 13 it wouldn’t be surprising to see him pop up again – he appeared to escape his doom in the series 12 finale and has unfinished business with Whittaker’s Doctor – and the fact that Sacha Dhawan has recently been spotted in Cardiff (where Doctor Who is currently filming) doesn’t exactly hurt this theory.

Read more: Sacha Dhawan "would really love" Doctor Who comeback as The Master

Of course, the SWARM theory isn’t foolproof, and while it fits very closely it could still be a coincidence, like when John Simm’s Mister Saxon was unintentionally an anagram of "Master No. Six" back in 2007. Plus, with rumours that the Daleks could also be in for a return this series and with six episodes to fill, the short list of monsters in the “Swarm” anagram starts to seem a little confining the more you look at it.

Still, there’s something about how well this all fits that does make us keen to look out for a missing M-monster in the coming weeks. If it does turn out to be true, credit where credit’s due – Chris Chibnall is the master of riling up internet commentary.

Doctor Who returns to BBC One on Sunday 31st October. For more, check out our dedicated Sci-Fi page or our full TV Guide.