In the waning days of the Time War, the Doctor tires of the constant fighting and bloodshed. He breaks into the Time Lords’ Omega Archives, containing forbidden Gallifreyan superweapons (most of which have already been unsuccessfully deployed against the Daleks). He takes the Moment, a galaxy-devouring weapon of mass destruction which has never been used because its sentient operating system has developed its own conscience, and will stand in judgement over whoever might try to use it. The Doctor abandons his TARDIS and sets off on foot to a bombed-out structure in the wastelands of outer Gallifrey, fully intending to activate the Moment and end the war. He’s puzzled when a young woman appears suddenly and refuses to leave: this is the Moment’s conscience, ready to try to dissuade its operator. It has chosen the appearance and voice of one of the Doctor’s companions, but has gotten past and future mixed up. The Moment offers to show the Doctor what will happen to him after he destroys Gallifrey…
Clara, having taken a job at Coal Hill School, gets a message from the Doctor and sets out to find the TARDIS. Moments after the time travelers are reunited, the TARDIS lurches unexpectedly, thanks to the UNIT helicopter that has grappled it and is hauling it toward the center of London. With the TARDIS now relocated to the National Gallery, Kate Lethbridge-Stewart shows the Doctor why UNIT need his expertise: a number of paintings, exhibiting an unusual three-dimensional effect, have had their glass frames broken from within; all of the paintings also once had humanoid figures in them, but those figures are now missing. Before the Doctor can investigate, a time fissure appears in mid-air in the Gallery, and he leaps through it, finding himself face-to-face with his tenth incarnation, who is dealing with a shapeshifting Zygon attempting to impersonate Queen Elizabeth I. And moments later, both Doctors are stunned – and alarmed – when another of their incarnations emerges from the fissure: an older man who does not regard himself as the Doctor. This is the incarnation of the Doctor who fought in the Time War, ending it in a pyrrhic stalemate that wiped out both the Time Lords and the Daleks, the incarnation that the later Doctors refuse to acknowledge; the Doctor’s true ninth life. The Queen orders all three of them taken away to the Tower of London.
In the modern day, the Tower is now UNIT’s headquarters, and the home of the Black Archive, a top secret repository of captured alien technology that would rival Torchwood’s collection. Kate and Clara return to the Tower, but it’s not until she is trapped in the Archive that Clara realizes that Kate has already been kidnapped and replaced by a Zygon. Grabbing a portable time manipulator that UNIT once took off of the briefly-dead body of a man named Captain Jack Harkness, Clara makes her escape, travels back to the past and rescues the three Doctors as well. The Doctors manage to thwart the Zygon invasion, but then the Doctor from the Time War vanishes. The tenth and eleventh Doctors follow him back to Gallifrey’s past – a place and time that the TARDIS shouldn’t be able to visit – and offer to help him activate the Moment so he doesn’t have to bear the consequences alone.
But the Doctor’s later incarnations, having struggled with the remorse of this act for hundreds of years, take the unprecedented decision to change history: save Gallifrey while allowing the Daleks to be destroyed, without interrupting their own timeline. But to save the Time Lords, more Doctors will be required – perhaps even Doctors who have yet to exist – and Gallifrey will have to be forcibly relocated, possibly into a parallel universe, leading to the impression that it has been destroyed. And even the Doctors’ attempt to save their home planet may still lead to its destruction.
written by Steven Moffat
directed by Nick Hurran
music by Murray Gold
Cast: Matt Smith (The Doctor), David Tennant (The Doctor), Christopher Eccleston (The Doctor), John Hurt (The Doctor), Paul McGann (The Doctor), Sylvester McCoy (The Doctor), Colin Baker (The Doctor), Peter Davison (The Doctor), Tom Baker (The Doctor), Jon Pertwee (The Doctor), Patrick Troughton (The Doctor), William Hartnell (The Doctor), Jenna Coleman (Clara), Billie Piper (Rose), Tristan Beint (Tom), Jemma Redgrave (Kate Stewart), Ingrid Oliver (Osgood), Chris Finch (Time Lord Soldier), Peter de Jersey (Androgar), Ken Bones (The General), Philip Buck (Arcadia Father), Sophie Morgan-Price (Time Lord), Joanna Page (Elizabeth I), Orlando James (Lord Bentham), Jonjo O’Neill (McGillop), Tom Keller (Atkins), Aidan Cook (Zygon), Paul Kasey (Zygon), Nicholas Briggs (voices of the Daleks and Zygons), Barnaby Edwards (Dalek 1), Nicholas Pegg (Dalek 2), John Guilor (Voice Over Artist)
Notes: The War Council shouldn’t be surprised at all that the Doctor can access the Omega Archives; his seventh incarnation was shown to be in possession of Time Lord superweapons that had presumably been with him for quite some time (Remembrance Of The Daleks‘ Hand of Omega and the living metal validium from Silver Nemesis, both aired in 1988). The Moment, first mentioned in The End Of Time Part 2 (2010), most closely resembles validium, but the Nemesis statue carved from validium had no obvious sign of a conscience, but did show signs of sentience.
The Zygons, though a popular monster in Doctor Who fandom, have only been seen in one prior television adventure, the Tom Baker era four-parter Terror Of The Zygons 
(1975), though they have reappeared in novels and numerous times in the eighth Doctor’s audio adventures, and even have their own action figure – not bad for a one-off villain.
This story seems to necessitate a reshuffling of the Doctor’s playlist: the incarnation commonly believed to be the ninth Doctor is actually the tenth, the tenth Doctor is actually the eleventh, and the current incarnation played by Matt Smith is actually the twelfth. This means that the incarnation to be portrayed by Peter Capaldi – glimpsed very briefly in the scene in which all of the Doctors rush to Gallifrey’s rescue – is the Doctor’s thirteenth and final life… unless, of course, the Doctor has somehow used up another regeneration somehow.
Asthmatic UNIT scientist Osgood may or may not be related to Sergeant Osgood, who served under Brigadier Lethbridge-Stewart in The Daemons (1971). UNIT’s Black Archive was 
established in the Brigadier’s final televised appearance, in the Sarah Jane Adventures two-parter Enemy Of The Bane, though it was not in the Tower of London at that time, meaning that the Black Archive has either been moved, or has a decentralized series of locations. Voice artist John Guilor, who had already provided the voice of the first Doctor in bonus features for the DVD release of 1964’s Planet Of Giants, reprised that voice for the every-incarnation-of-the-Doctor climax.
Whether you consider his final appearance to have occurred in 1981’s Logopolis or the 1993 charity special Dimensions In Time, this episode marks Tom Baker’s first appearance in new footage in 
televised Doctor Who in a very long time; the exact nature of his character is left extremely vague.
One day after its premiere unfolded simultaneously in 94 countries, The Day Of The Doctor and its production team were awarded the Guinness World Record for the most widely watched non-news, non-sports drama presentation in the history of the medium of television.
LogBook entry & review by Earl Green
As the Doctor shows off his latest innovation to Jamie and Zoe – a rudimentary gauge added to the console to show the year in which the time machine has landed – just as the TARDIS is dragged off course violently. It makes an emergency landing on a planetoid in orbit around a pulsar whose gravitational effects on local spacetime pulled the TARDIS here. An ancient city lies nearby, with a human expedition puzzling over what is found there – and something is slowly stalking that expedition. The Doctor recognizes it as an entity capable of manipulating time, and braces himself to sacrifice years of his own life to save his friends.written by Simon Guerrier
The Doctor is startled when a flashing red light appears on the TARDIS console. The surprise isn’t that the light has never flashed before, but that it is there at all, where there was no light on the console before. And it’s not just one Doctor, but all of the Doctor’s incarnations.