In "The Caretaker," we take an unorthodox step; rather than showing the Doctor spiriting his companion away to a faraway spot in space and time, we see him going in the opposite direction, paying a visit to her daily life.

Naturally he doesn't quite manage to fit in, although given his past history with Coal Hill school, and his years of experience mopping up alien messes, he should be better equipped for his new job than he is.

Here are a few things to keep an eye out for, the next time you watch:

(The episode is available on iTunes and Amazon.)

Gareth Roberts first started writing the story before Peter Capaldi had been announced as the Twelfth Doctor, and certainly before he had any idea what the character would be like. He told Cultbox that he asked Steven Moffat for some pointers and received some invaluable clue: "One of the key things I got from Steven at the early stages was to think of an early Tom Baker, the sort of 'Arc in Space' or 'Genesis of the Daleks' Tom Baker, who’s quite stern and remote, but also very funny. The Doctor is always going to want to say the wrong thing."

This isn't the first time we've seen the idea of the Doctor working as a caretaker at Coal Hill School (where his granddaughter Susan got her Earth education). In "Remembrance of the Daleks" the Seventh Doctor is asked by the 1963 Headmaster of the school whether he is there to apply for the position, who notes, "you're a bit over-qualified for the position, but if you would like to leave your particulars and references."

Clara mocks the Doctor's assertion that he can hide in "deep cover", asking, "Where, the Magic Circle?" This is a reference to a British association of stage magicians, formed in 1905. To join, magicians must either pass a practical exam, or a written thesis on a particular branch of stage magic. The magic circle has a hierarchy too; rank and file members are called Members of the Magic Circle, then there are Associates of the Inner Magic Circle, and Members of the Inner Magic Circle, both affiliated to an elite core of 300 magicians.

The Doctor claims that the Skovox Blitzer has been drawn to the area by "artron emissions". According to events in the Fifth Doctor story "Four to Doomsday," artron energy is a residue from the Time Vortex which also helps to power TARDISes. It's also something that travelers in time will pick up along the way, like background radiation, so in fact the Blitzer is chasing the residue left by the Doctor.

Eagle-eyed fans of classic Doctor Who have spotted that there is a banner hanging on the wall reading "A Spirit of Adventure." In the First Doctor story The Sensorites, the Doctor looks back on their recent adventures admiringly, saying, "It all started out as a mild curiosity in a junkyard, and now it's turned out to be quite a great spirit of adventure, don't you think?"

There's a little nod within the script to Jenna Coleman's other work. Her role as Lydia Wickham in the Jane Austen sequel Death Comes to Pemberley was first broadcast around the end of the previous series of Doctor Who, and in this story, Clara's class are reading out a section of Pride and Prejudice which refers to Lydia.

https://www.youtube.com/watch?v=BzezYWDb0zI

If it looks like the Doctor has a specific species in mind when he refers to "fish people," that's because his Second Incarnation met with a species of people in the underwater city of Atlantis who had been modified so they could breathe underwater.

It's curious that the Doctor should be so emphatic that a former soldier cannot possibly teach mathematics, given that this is the exact subject that his very dear friend the Brigadier taught when he retired from running UNIT. His Fifth incarnation seemed a lot less bothered about the move from soldier to mathematician when they met in 1983's "Mawdryn Undead."

Whether intentionally or not, there's a neat echo of a line from the Second Doctor's first ever story, "The Power of the Daleks" in a moment between the Doctor and Danny Pink. Seeking to close down a conversation, he turns to Clara and says "Shut him up, shut him down. Up or down, it doesn't matter to me. I've got a lot of work to do." In "The Power of the Daleks," the Doctor demands "These lumps of metal, Daleks, I want them broken up, or melted down. Up or down, I don't care which, but destroyed!"

The Doctor is heard whistling "Another Brick in the Wall (Part 2)" by Pink Floyd, a song complaining about brutal teachers, which begins "we don't need no education."

https://www.youtube.com/watch?v=HrxX9TBj2zY

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