As well as bringing together multiple incarnations of the Master, this story both explained and depicted the genesis of the Ravenous, inadvertently caused by the ancient Time Lord engineer Artron, as well as their end, by Artron's own command, as he returns them to their Kolstani forms.
By visiting Artron around the time of his discovery of artron energy, and before the start of the Rassilon Era, this story depicts Time Lord history at an early point in their history along with Collision Course, which featured the first prototype TARDIS while this one features a fleet of battle TARDISes placing it afterwards.
Liv Chenka and all others within the same time zone temporarily gain the ability to regenerate, like Time Lords, but indefinitely, and without changing form. The man who granted Helen's wish in Fairytale of Salzburg is also revealed to have been Artron.
With regards to the Master's timeline, Day of the Master finally explains how the maniacal Time Lord's twelfth and final regeneration, once more in decay, managed to acquire a new regeneration cycle. Three incarnations of the Master watch as he regenerates into a familiar body.
The Doctor investigates a mystery in the vortex, Liv follows the trail of their enemy, and Helen searches for a god. Everywhere they go there is a Master or Mistress, but is the Doctor's oldest enemy there to hinder them, or to help? With the TARDIS crew scattered and lost, only a miracle can save the universe. And for that to happen someone is going to have to die.
Badly injured, and upset about what the Ravenous are doing to the TARDIS, the Doctor is nevertheless persuaded by Liv to escape with the Master's TARDIS. Once they're on board, the Doctor uses the scanner to track Helen down, but finds no sign of her or Eleven on the planet. Liv insists that they go after the Eleven, thinking that Helen is with him, but the Doctor says that they can't. Since the Eleven travels with the Ravenous, it's impossible to track him down this time. Rather, the Doctor checks the information that Eleven and the Master were looking for in Artron's tomb: the coordinates of a planet, Kolstan, whose existence is supposed to be impossible.
The Doctor tricks Liv by abandoning her at an apparently deserted Time Lord waiting station. He tells her that the journey he must undertake will take him all the way to the prehistory of Gallifrey: too dangerous for her. After sending out a distress signal for other Time Lords to come to her rescue, the Doctor sets off.
Meanwhile, on a devastated and abandoned Earth of the future, Helen is forced by "Missy" to read an ancient book, one that the Time Lady can't decipher. Together, the two women travel to a tower to meet what the book describes as a "god" come to Earth in prehistoric times with his servant. Missy forces Helen to follow her at gunpoint, but Helen imagines that the reason she cannot read the book is because the "god" does not want her to. The book tells what they're doing in the exact moment they do, almost as if predicting the future - which Missy explains it's due to the fact it irradiates temporal energy.
The Doctor arrives on Kolstan, where he is rescued by Artron, the great Gallifreyan scientist. He manages to cure the Doctor (who pretends to be from Earth so as not to reveal details about the future) by exploiting the planet's energy, and then explains the special nature of the place. The inhabitants, the Kolstani (a primitive species with a limited language), feed on the energy of the Time Vortex. With this they created the planet they live on, and with this they have taken on the power to heal all wounds, even the most serious. Artron is here to study this ability of theirs, and potentially replicate it on the Gallifreyans. The Doctor is not convinced of the idea: it is too great a power to give to those who would potentially misuse it. Their conversation is interrupted by the "Bruce" Master, who has been assisting Artron in his experiments for some time, pretending to have been sent from Gallifrey.
At the station, Liv is joined by the 'War' Master. Without revealing his identity, he listens to what she has to say, meanwhile 'putting the pieces together'. He explains to her the nature of Kolstan as a planet located in the centre of the Vortex, considered a legend by his people. Liv proposes to get to the Doctor, but the Master replies that it's impossible: his TARDIS, being a new model, can't travel that far back in time without being specially programmed. Instead, he replies that it's better to listen to the internal communications network in Gallifrey and wait for a distress call. That's the station that's likely to be attacked by Eleven and the Ravenous, and then they can reach them.
Helen and Missy, after a long journey, finally arrive at the foot of a tower. They try to get in, but a force field keeps Missy out, allowing only Helen access. Helen starts to climb the stairs of the tower, but at one point on the way up a voice from above asks her if she has come to find a god. Then, without warning, Helen is lifted into the air and thrown down: the god does not want to see her.
On Kolstan, the "Bruce" Master shoots one of the Doctor's hearts, and forces Artron to provide him with Kolstani energy if he wants to save him. Artron accepts, but uses the equipment built by the Master to absorb the Kolstani power himself. This makes him extremely powerful (and he does indeed cure the Doctor immediately), but it also breaks his mind; moreover, with the Kolstani deprived of their energy, the planet begins to collapse. The Kolstani themselves begin to feel "hungry", and then the Doctor realises he's witnessing the birth of the Ravenous. Artron and the Doctor try to escape in the Master's TARDIS, but the "Bruce" Master was faster. The two then find themselves marooned on Kolstan, while a fleet of Gallifreyan warships arrives to attack the planet.
The "War" Master and Liv arrive on the Crucible of Souls, where the Eleven and the Ravenous have slaughtered the crew. Regardless of the attack, the Master proceeds with Liv to the control room, where they observe the Eleven "reverse the polarity" of one of the mechanisms, using Artron's brainprint. On the way back to the TARDIS, the Master reveals that he no longer needs Liv: he only kept her as collateral, to be fed to the Ravenous to save himself in case of need. He also reveals to her that he is the Master, before shooting her with a World War I human gun. But to the amazement of the Master and Liv, she heals immediately - and begins to regenerate.
Using the Crucible of Souls and Arctron's brainprint, the Eleven has given every species in the universe the ability to regenerate. Every people on every planet is now a source of food for the Ravenous as they are free to feed and multiply. When they will be done, the only living beings living in the universe will be the Ravenous and the Eleven.
On Kolstan, about to be attacked and destroyed by the Gallifreyan war fleet sent by Rassilon, the Doctor comments that on days like this he wishes he'd stayed at home. Misinterpreting his words, Artron transports them both to prehistoric Earth. The Doctor then realises that he, Liv and Helen have already met Artron, in Salzburg. It was he who summoned the Krampus and he who rejuvenated Helen, in both cases granting a wish. The Doctor proceeds to tell him how by saving his life Artron unwittingly created the Ravenous; now that they lack the energy of the Vortex, the Kolstani will go and feed on the closest things to it, regenerative energy. The Doctor mysteriously disappears while he is still talking.
On future Earth, Artron - the "god" Missy was looking for - recognises Helen from Salzburg, and after stopping her fall, allows her to come and see him. He tells her about what happened with the Doctor, and Helen understands why Missy could not read the book: as a Time Lord, it is written in a language older than her own. He tells her about what happened with the Doctor, and Helen understands why Missy could not read the book: as a Lady of Time, she cannot read a language older than her species. At that moment, Missy shoots Artron, stunning him, and then starts shooting Helen as well to kill her. He tells her about what happened with the Doctor, and Helen understands why Missy could not read the book: as a Lady of Time, she cannot read a language older than her species. At that moment, Missy shoots Artron, stunning him, and then starts shooting Helen as well to kill her.
On the Crucible, Liv forces the "War" Master (by shooting him in the arm) to take her to the Doctor, but he tricks her into taking them both back to the waiting station where he found her. There they find the "Bruce" Master, who arrived there using the now unusable "Decayed" Master's TARDIS fast return switch. Together, the two Masters defeat Liv and, while "War" contacts Gallifrey, "Bruce" attempts to throw her out, into space. Just before he succeeds, however, the Doctor and Helen stun him, saving Liv. Helen reveals that she wished to reunite her with her friends, and Artron granted her wish by having them meet her there; Liv in turn tells of what the Eleven did. The trio then decide to steal the "War" Master's TARDIS and travel to the Crucible, in an attempt to undo what the Eleven has done.
The "War" Master only realises what has happened after making a deal with the CIA, and is therefore forced to send a distress signal so that another incarnation of the Master can intervene and help them. "Missy" answers the call and, after the three Masters agree upon fulfilling the bargain, brings them Artron. He then contacts the Eleven, offering them a deal: they will hand over Artron to him and the Ravenous, in exchange for immunity from the Ravenous. The rendezvous is at the Crucible.
At the now deserted Crucible, the Doctor, Liv and Helen find the TARDIS, brought there by the Ravenous as spoils of war. In secret, they witness the meeting between the Eleven, the Ravenous and the "Bruce" Master, sent ahead because he was "indigestible" to the creatures' hunger. The Master frisks Eleven, then hands him Artron and leaves. The Ravenous seem to recognise Artron, and the Doctor begins to formulate a plan, just as the Ravenous discover their presence.
In another room of the Crucible, the Masters set up a camera so they can watch the Doctor interact with the Eleven and the Ravenous. Under the guise of searching the Eleven, the "Bruce" Master has actually stolen Artron's brainprint, which they have to take back to Gallifrey. Meanwhile, the "War" Master has undone what the Eleven has done, removing the ability of the universe's species to regenerate.
In the control room, the Ravenous attack the Doctor, but Liv gets in the way, allowing herself to be sucked off regenerative energy. The Doctor reaches Artron, and convinces him to express his own wish: to make amends for what he's done, bringing back the Kolstani. Artron grants himself his wish, giving the Ravenous back the energy he took from them, and returning them to their original Kolstani form. Meanwhile, the "War" Master has undone what the Eleven has done, removing the ability of the universe's species to regenerate.
In the control room, the Ravenous attack the Doctor, but Liv gets in the way, allowing herself to be sucked off regenerative energy. The Doctor reaches Artron, and convinces him to express his wish: to make amends for what he's done, bringing back the Kolstani. Artron then grants himself his wish, giving the Ravenous back the energy he took from them, and returning them to their original Kolstani form. The effort kills him, but before he dies Artron is forgiven by the Kolstani: he can then expire in peace. At that moment, another Gallifreyan war fleet, alerted by the Masters, attacks the Crucible to destroy it.
The Doctor, Liv and Helen manage to escape with the badly damaged TARDIS. The Eleven tries to escape with the Master's TARDIS, but finds the three Masters waiting for him. He tries to offer them an alliance, but after pretending to accept, the three shoot him (once each) and throw him out, leaving him on the Crucible. After trying in vain to heal himself with Artron's brainprint stolen by the Masters, the Eleven regenerates in defeat.
The three Masters go to Parrak, to Artron's tomb. In exchange for their help, the CIA allowed them to use the brainprint to bring their "Decayed" past incarnation back to life and grant him a second regenerative cycle. Posing as CIA agents, the three cause the "Decayed" to regenerate into a new incarnation.
- The Doctor - Paul McGann
- Liv - Nicola Walker
- Helen - Hattie Morahan
- The Eleven/The Eleven - Mark Bonnar
- The Master - Eric Roberts, Derek Jacobi and Geoffrey Beevers
- Missy - Michelle Gomez
- Ravenous 1 / Kolstani 1 - George Asprey
- Ravenous 2 / Kolstani 2 / Valcon - Susie Emmett
- Artron / Cadrin - Robert Whitelock
- In Artron's time, Rassilon is still experimenting with regeneration.
- When working out his identity, Liv believes the War Master to be an incarnation of the Eleven, guessing he is the Twelve, the Thirteen, the Four, or the Six, in that order.
- The Doctor thinks Missy could be an incarnation of the Rani, saying that the Master and the Rani have worked together in the past.
- When the War Master suggests wiping the "Bruce" Master's mind and throwing him into the vortex, Missy mentions River Song, and states that she wouldn't object to trying her methods of mind wiping on the "Bruce" Master.
- The "War" Master and Missy agree they'll have to throw out the "Bruce" Master in the Vortex again when they're done, so to preserve the timeline.
- The Doctor briefly assures himself he has no need to regenerate, and then wonders if he is still fit to do so after his attack from the Ravenous.
- Regarding the War Master and Missy being in Ravenous 4, Dorney said there would be no amnesia involved. Indeed, the Doctor never meets them in person, nor does he learn they are future incarnations of the Master. Although Liv describes the War Master, and identifies him by name, the description is sufficiently vague for the Doctor to muse that it could be any Master, while Helen only ever discovers Missy is a Time Lady who knew the Doctor, leaving the Doctor to theorise that she may be the Rani.
- Day of the Master was recorded on 28 February 2019. On the same day, John Dorney reported on the recording of "a dark little scene, done by two brilliant actors", that was "going to upset people". Also, according to Dorney, episode 1 of Day of the Master featured the "best cliffhanger [he] ever [wrote]".
- The Doctor notes that the Master and the Rani have worked together in the past. (TV: The Mark of the Rani)
- River Song once teasingly mistook Missy for the Rani. (AUDIO: The Bekdel Test)
- The Crucible of Souls is used by the Ravenous and the Eleven in their grand plan. The Crucible was previously a part of a plan by the Nine and the Doom Coalition. (AUDIO: The Crucible of Souls)
- The War Master is granting his past self a new regeneration cycle as part of a deal with the CIA. (AUDIO: The Devil You Know)
- The War Master declares that his past self would have "a new body, at last". (TV: The Keeper of Traken)
- Missy says "Hello you" to the "Bald" Master. (AUDIO: Dominion)