The Doctor, Yaz, and Dan intercept a Cybermaster attack force as it launches an assault on a hyperspace train. The Cybermasters are targeting a container holding a Gallifreyan girl. During the battle, Dan barely survives a breach of his spacesuit helmet, and decides to leave the TARDIS and resume a life that, while it may be less exciting, is also far less dangerous. On Earth, former time travelers Ace and Tegan now work for UNIT, each of them chasing down different unusual events: Tegan is trying to retrace the steps of seismologists who have gone missing, while Ace is investigating a series of paintings that have been abruptly removed from public display. The Doctor receives a warning from a Dalek of an imminent attack on Earth, and, surprisingly, an offer of information to prevent that attack. But the message ends before any useful information can be conveyed, and the Doctor’s attention returns to tracking down the Gallifreyan child… and the fact that there’s suddenly an extra planet near Earth’s orbit in the year 1916 – the same year in which the Master is posing as Rasputin in Russia.
The Doctor and Yaz visit the extraneous planet, finding that the Gallifreyan child is simply a disguise employed by a Qurunx, a powerful sentient energy being chained to a Cyber-conversion planet by the Master and the Cybermen. But before the Doctor can unravel that mystery, the TARDIS is summoned to UNIT HQ in 2022, where Kate Lethbridge-Stewart needs the Doctor’s expertise on the parallel mysteries of the missing paintings and missing seismologists, which seem like a distraction from the events in 1916…until the Master’s hand is detected in the disappearances as well. The Doctor is briefly, awkwardly reunited with Ace and Tegan, but soon resumes the chase, tracking down the Master in Naples, and discovering he is responsible for killing the missing seismologists. UNIT takes the Master into custody, but this is exactly what he wants, as this allows him to bring an entire Cyber invasion force directly into UNIT HQ. The Doctor and Yaz, however, have already left again, once again following a lead from the Dalek’s message, leaving Ace and Tegan to try to help fend off the Cyberman attack. As Yaz anticipates, the Dalek message proves to be a trap. The Doctor is taken back to 1916 Russia, where the Master instigates a forced regeneration during which his consciousness is forced into the Doctor’s body, as Yaz is helpless to watch.
But the Doctor’s friends and allies, past and present, are legion. Yaz, with help from Vinder, Ace, and Graham, and with some helpful advice from a hologram of the Doctor, reverses the forced regeneration and thwarts the Daleks’ plan, and arrive just in time to see Tegan and Kate Stewart end the attempted Cyberman invasion. Even the Qurunx is freed. As the Doctor’s former companions return to their normal lives, Yaz prepares to return to hers, as the Doctor’s body, as a result of the trauma caused by the forced regeneration, is once more wearing a bit thin.
written by Chris Chibnall
directed by Jamie Magnus Stone
music by Segun Akinola
Cast: Jodie Whittaker (The Doctor), Mandip Gill (Yasmin Khan), John Bishop (Dan Lewis), Sophie Aldred (Ace), Janet Fielding (Tegan Jovanka), David Bradley (The Doctor), Colin Baker (The Doctor), Peter Davison (The Doctor), Paul McGann (The Doctor), Sylvester McCoy (The Doctor), Jo Martin (The Doctor), David Tennant (The Doctor), Sacha Dhawan (The Master), Jemma Redgrave (Kate Stewart), Jacob Anderson (Vinder), Bradley Walsh (Graham O’Brien), Patrick O’Kane (Ashad), Joe Sims (Deputy Marshal Arnhost), Sanchia McCormack (Train Marshal Halaz), Danielle Bjelic (Curator), Anna Andresen (Alexandra), Richard Dempsey (Nicholas), Jos Slovick (Messenger), Nicholas Briggs (Dalek voices / Cybermen voices), Barnaby Edwards (Dalek), Nicholas Pegg (Dalek), Simon Carew (Cyberman), Jon Davey (Cyberman), Chester Durrant (Cyberman), Mickey Lewis (Cyberman), Felix Young (Cyberman), Richard Price (Cyberman), Andrew Cross (Cyberman), Matt Doman (Cyberman), Bonnie Langford (Melanie Bush), Katy Manning (Jo Jones), William Russell (Ian Chesterton)
Notes: This marks the first televised appearance of Tegan and Ace since their final TV appearances, in Resurrection Of The Daleks (1984) and Survival (1989), respectively. Dialogue for both characters seems to contradict adventures chronicled in other media. Ace says the last time she saw the Master, he was “half cat” (which would seem to indicate she hasn’t seen him since Survival, contradicting the New Adventures novel First Frontier); Tegan hasn’t seen the Doctor in 38 years, contradicting the Big Finish audio story The Gathering, which reunited an older Tegan with the fifth Doctor in 2006. However, the Master’s description of Ace’s eventual falling-out with the seventh Doctor lines up well with both the 1992 New Adventures novel Love And War and the later Big Finish audio adaptation of that novel, so perhaps this is something to blame on the wibbly-wobbliness of time. Tegan and Ace aren’t the only companions making their first appearances in a very long time; Melanie was last seen in Dragonfire (1987), and Ian Chesterton was last seen in The Chase (1966), winning William Russell the official Guinness World Record for the longest time between television appearances as the same character (56 years). Jo Jones (formerly Jo Grant), on the other hand, had made a relatively recent appearance in The Sarah Jane Adventures (The Death Of The Doctor, 2011). All of these actors, however, have been reprising their roles for Big Finish audio productions for many years. The Doctor says the Master couldn’t “corral Daleks and Cybermen” (see also: Frontier In Space and The Five Doctors, respectively). The Master also tried to forcibly steal the Doctor’s body in the 1996 TV movie, though in that instance the process was interrupted. Other than being the finale for Jodie Whittaker’s Doctor and Chris Chibnall as showrunner, The Power Of The Doctor was also intended to celebrate 100 years of the British Broadcasting Corporation.
LogBook entry by Earl Green
Cast: Jodie Whittaker (The Doctor), Bradley Walsh (Graham O’Brien), Tosin Cole (Ryan Sinclair), Mandip Gill (Yasmin Khan), Alan Cumming (King James), Siobhan Finneran (Becka Savage), Tilly Steele (Willa Twiston), Tricia Kelly (Old Mother Twiston), Arthur Kay (Smithy), Stavros Demetraki (Alfonso)
Cast: Jodie Whittaker (
Notes: 
Cast: Jodie Whittaker (
Notes: The Doctor attempts to call 
Cast: Jodie Whittaker (
Notes: Sacha Dhawan has plenty of Doctor Who history, most notably starring as Waris Hussein in the 50th anniveresary docudrama 
Cast: Jodie Whittaker (
Notes: The Master has resumed use of his signature weapon, the Tissue Compression Eliminator, which made its debut alongside the Master himself (Terror Of The Autons, 1971); it was last seen when another incarnation of the Master was trying to “improve” it (Planet Of Fire, 1984). The “knock four times” rhythm that drove a previous incarnation of the Master insane resurfaces here (featured heavily in 2007’s The Sound Of Drums and both parts of 2009’s The End Of Time). Gallifrey was forced into a pocket universe in 2013’s Day Of The Doctor for its own protection at the end of the last great Time War, though a later incarnation of the Doctor visited it in Hell Bent (2015); as it turns out, Gallifrey didn’t stand very long. The real Ada Lovelace went on to develop a correspondence with the real Charles Dickens (a fictionalized version of Dickens met the ninth Doctor in 2005’s The Unquiet Dead; it’s probably safe to assume that they never compared notes about their strange friend with the time-traveling blue box, since the Doctor wipes Ada’s memory of their shared adventure here).