The episode stars Jodie Whittaker as the Thirteenth Doctor, alongside Mandip Gill and John Bishop as her companions, Yasmin Khan and Dan Lewis, respectively.
In the Temple of Atropos, the Doctor jumps into the time storm and stalls Swarm by hiding Dan, Yaz, and Vinder in their pasts.
Bel, a survivor of the Flux, evades the Daleks in a forest, finds a Lupari ship and weapons, and escapes to the Cybermen sector.
Swarm appears in his original form and has vessels called Passengers each storing hundreds of thousands of life essences.
[15][16] Overnight the episode was watched by 3.76 million viewers; it was the fourth most-watched programme of the day only behind Strictly Come Dancing, Top Gear, and Countryfile.
"[10] The Independent's Isobel Lewis agreed, calling it a "meaningless mess", but said there were some "hopeful moments" among the "bewildering plotlines.
"[12] Meanwhile, Michael Hogan with The Telegraph disagreed, believing that the "disorienting" and "woozy, trippy narrative" of the episode was the overall goal and that it was "jam-packed with treats for the fans.
"[13] Caroline Siede similarly praised the episode writing that "one of the things “Once, Upon Time” does best is evoke a dream-like sense of confusion".