For the Doctor, the stakes have rarely been higher than they are in "World Enough and Time." He's on the brink of regeneration, his companion has been converted into a proto Cyberman and his project to encourage Missy to take a different path in her life is likely to suffer a knock when she meets her former incarnation.
The whole story is far from over, but in the meantime, here are a few things to keep an eye out for, the next time you watch:
The title is a reference to the poem To His Coy Mistress by Andrew Marvell. This is a love poem pondering on the distorting effects of love on the perception of time, which also features the title of another recent Doctor Who story—"Before the Flood".
"Had we but world enough and time,
This coyness, lady, were no crime.
We would sit down, and think which way
To walk, and pass our long love’s day."
And, in a devotional section he goes on to say:
"My vegetable love should grow
Vaster than empires and more slow;
An hundred years should go to praise
Thine eyes, and on thy forehead gaze".
It's tempting to conclude that the Doctor had this section in mind when tutting "finally, it's like watching plants grow" at the beginning.
Two items of British cuisine appear in this episode—or three, if you count the good tea/bad tea. The Doctor spends his time in the TARDIS eating "crisps," which are of course the British name for potato chips. And Missy also believes that beans on toast are a pan-human meal, rather than merely a staple of the British diet.
You may have heard the voice of Oliver Lansley, who played the blue-faced Jorj, before, as he also appeared as Jack Ridpath in series thirteen of the the Big Finish audio adventures Jago & Litefoot.
Although the Master's reference to a "genesis of the Cybermen" was an obvious nod to the classic 1975 Doctor Who story "Genesis of the Daleks," there was a story planned which explored the full origins of the Mondasian metal men. And actually, there have been several origin stories for the Cybermen across various Doctor Who media. The Tenth Doctor saw the beginnings of the Cybus industries Cybermen in "Rise of the Cybermen" / "The Age of Steel", which was partly based on the Big Finish Fifth Doctor story "Spare Parts". And two Doctor Who comics have told the story of the Cybermen - "The World Shapers" and "The Cybermen".
Clearly relishing putting the cat among the pigeons, Steven Moffat having Missy introduce herself as "Doctor Who" plays into a common fan argument about why the show is called Doctor Who when the Doctor is just the Doctor. While it's apparent that he doesn't really consider his name to be Doctor Who, the Doctor has referred to himself with that name during the lifetime of the show. In "The Highlanders" the Second Doctor calls himself "Doktor von Wer" (or "Doctor of Who" in German), and in "The Underwater Menace," he signs a note "Dr. W". The Third Doctor's car "Bessie" had various personalized numberplates, all starting with the letters WHO, and he introduced himself as "the great wizard Qui Quae Quod" (a very fitting three variations on "Who" in Latin). Even as recently as "Rose", the website whoisdoctorwho.co.uk asked "Who is Doctor Who?", leaving the question of whether Doctor Who is a canonical item of nomenclature or just a passing question entirely open.
Those speedy inertia lifts are only a step up from the inertia corridor through which the Fourth Doctor travels at some speed in "The Pirate Planet." When he arrives, the Doctor vows "never to be cruel to an electron in a particle accelerator again." It's another of this season's nods towards Douglas Adams (who wrote the script for that story).
A common Time Lord trait is the inability to judge human degrees of physical attractiveness, as Missy does while attempting to "flirt" with Jorj. So while the Twelfth Doctor struggled to age Clara, the Sixth referred to his companion Peri as "ugly" ("Timelash"), the Ninth said Rose Tyler was beautiful "for a human" and the Fourth told Countess Scarlioni that she was “a beautiful woman, probably” in "City of Death."
It seems that whenever the Doctor has to explain Gallifrey and the Master to his companions, he chooses to do so while eating chips outdoors. His scene with Bill echoes a very similar moment during "The Sound of Drums," in which he and Martha and Captain Jack were enjoying a fish supper and discussing old times:
Venusian martial arts were a key aspect of the Third Doctor's adventures. Whether aikido or karate, he would regularly flip combatants over to disarm them, in such adventures as "Inferno," "Colony in Space," "The Mutants," "The Green Death," and "The Time Warrior." And Nardole's reference to four arms is a nod to the celebrated Target novelizations of Doctor Who stories, which would often point out that the Doctor's proficiency was a rare achievement for a two-armed being.
In the classic series, it was relatively common for the Master to make his first appearance in disguise, and indeed, that's how he made his return to Doctor Who, in the very human form of Professer Yana in "Utopia." Some of his alternate identities have been less subtle than others, such as Colonel Masters in "Terror of the Autons", and the Reverend Magister (which is "Master" in Latin) in "The Daemons".
This need for subterfuge also extends to the billing of Anthony Ainley (who played the Master in many Fourth, Fifth, Sixth and Seventh Doctor stories) in TV listings magazines before the show aired. He has appeared under the name Neil Toynay (an anagram of "Tony Ainley") and James Stoker ("Master's Joke").
Now go back and read the entire 10 Things You May Not Know About Doctor Who archive.