Once, Upon Time
"Once, Upon Time", prefixed frequently with either "Chapter Three" or "Flux", is the third episode of the thirteenth series of the British science fiction television programme Doctor Who, and of the six-episode serial known collectively as Doctor Who: Flux. It was first broadcast on BBC One on 14 November 2021. It was written by showrunner and executive producer Chris Chibnall, and directed by Azhur Saleem.
The episode stars Jodie Whittaker as the Thirteenth Doctor, alongside Mandip Gill and John Bishop as her companions, Yasmin Khan and Dan Lewis, respectively.
Plot
With humanity now on the verge of extinction, the Daleks, Cybermen, and Sontarans occupy most of the remaining planets. In the Temple of Atropos, the Doctor jumps into the time storm and stalls Swarm by hiding Dan, Yaz, and Vinder in their pasts.Dan experiences his date with his love interest Diane, until the Doctor appears as a hologram and Swarm's companion Passenger abducts Diane. Yaz talks with her police partner and tries to teach her sister a video game, but sees the Doctor instead. Vinder reluctantly relives his time assisting the dictatorial Grand Serpent and his demotion to a remote outpost upon revealing the Serpent's misdeeds, with Yaz as his superior and the Doctor as a hologram. Vinder makes video messages aboard the outpost.
Bel, a survivor of the Flux, evades the Daleks in a forest, finds a Lupari ship and weapons, and escapes to the Cybermen sector. Bel kills a boarding party, then confesses her motivations to the last Cyberman she kills: she is searching for her lover, Vinder. Bel finds Vinder’s messages, and comforts their unborn child.
The Doctor jumps into her own timestream and recovers memories of her past Fugitive Doctor incarnation and three other Division officers, including the Lupari officer Karvanista, raiding the Temple to confront Swarm and Azure. Swarm appears in his original form and has vessels called Passengers each storing hundreds of thousands of life essences. The Fugitive Doctor has secretly hidden six powerful Mouri priests inside, and unleashes them.
Back in her present, the Doctor finds the priests and encourages them to return to the temple, but the priests forcibly separate her from her past memories to protect her from the time storm's effects. Awsok, a mysterious old entity, chides the Doctor, claiming the Doctor's mission is futile. Awsok reveals the Flux was deliberately created and placed and is the Doctor's fault.
The Doctor returns Yaz, Dan and Vinder to the present. Azure reveals they knew what the Doctor would do and brought her to Atropos on purpose. Swarm reveals Diane's entrapment in Passenger, and the Doctor and Vinder promise to help Dan get her back before Swarm, Azure and Passenger leave the temple. The Doctor uses the TARDIS to return Vinder to his ravaged home planet and gives him a device to contact her. After taking off, a Weeping Angel jumps out of Yaz's phone and seizes the TARDIS console.