This article contains spoilers for Doctor Who season 13, episode 1.
Doctor Who season 13, episode 1 confronts the Doctor with the threat of the Flux - a mysterious cosmic phenomenon clearly controlled by a being known as Swarm. Doctor Who season 13 is unlike any season since the classic BBC TV series was relaunched in 2005. Faced with production problems caused by the coronavirus pandemic, Doctor Who showrunner Chris Chibnall has chosen to tell the story in a very different way.
"Doctor Who is one of the most difficult shows to produce, and we were aware that [the pandemic] would make it even more difficult," Chibnall admitted in an interview in Doctor Who Magazine. "We've tried to keep pushing the show every year, and we didn't want to let the ambition of the show down. But to continue with the previous number of episodes was financially, logistically, and operationally impossible." And so Doctor Who season 13 is a single story running through six episodes - a serialized structure that will hopefully play to Chibnall's strengths.
In another surprising move, the BBC isn't marketing this as Doctor Who season 13. Rather, it's being called Doctor Who: Flux, named after a mysterious cosmic event that the BBC has been keeping under wraps. But Doctor Who: Flux episode 1 saw the Doctor stumble upon this cosmic phenomenon; here's everything she learned.
The Flux Is Destroying The Universe
According to the Doctor, the Flux is nothing less than the end of the universe itself. When the Doctor scanned it with the sonic screwdriver, she was horrified to learn it disobeys every law of time and space, disrupting every particle it comes into contact with. Visually, this is rendered as a strange boiling effect that manifests whenever the Flux encounters a planet or star. Although the Flux appears to be some sort of expanding wave, the TARDIS detected multiple signals, suggesting there are several Flux events being triggered across the universe.
The Flux Appears To Be Controlled By Swarm
The Flux is apparently controlled by a being who calls himself Swarm. Doctor Who season 12 revealed the Doctor had a history before the William Hartnell incarnation, one that stretched back to the dawning days of Gallifrey itself. At least one of these pre-Hartnell Doctors worked for a clandestine Time Lord agency called the Division, and it seems while acting as their agent the Doctor encountered this being called Swarm, who was imprisoned from the dawn of time until the present day. It's no coincidence the Flux begins when Swarm escapes at last, and when he has a face-to-face psychic confrontation with the Doctor he sends the Flux against her.
The Flux Can Be Repelled
The canine race known as the Lupari have successfully created technology that can repel the Flux's destructive effects. The Doctor persuades their leader Karvanista to have their entire armada protect the Earth in an interlocking pattern that completely shields the planet; but this is just one world. The Flux is destroying the entire universe, and Earth seems to be the only planet that will be saved.
The Sontarans Know About The Flux
Curiously, Doctor Who: Flux episode 1 reveals the Sontarans are aware of the Flux's existence. According to one of the clone warrior race, they expect the Flux to bring "incredible suffering, vast bloodshed, a conflict that will dwarf all that has come before." As one of the few time-aware races in the galaxy, the Sontarans are uniquely equipped to take advantage of the chaos caused by the Flux, and Doctor Who season 13, episode 1 ends with them launching an attack - presumably on Earth. The Flux has arrived in Doctor Who, and it has brought with it one of the most dangerous armies in the galaxy.