"Into the Dalek" is the Twelfth Doctor's first encounter with one of his oldest foes, and it's one of his more troubling meetings, closer in spirit to the Ninth Doctor's encounter in "Dalek" than any of the world beating battles he more commonly experiences.

It's the first chance to see a regenerated Doctor more fully in control of his faculties and trying out his new body and personality, and it shows a Doctor who is unafraid of rubbing people up the wrong way, even if he receives a similarly rough emotional journey from his Dalek host.

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

(The episode is available on iTunes and Amazon.)

There's a strong gaming connection to this story. Steven Moffat came up with the idea while talking over plans for a potential Doctor Who computer game, and the story was co-written by Phil Ford, who also wrote the Doctor Who adventure game "City of the Daleks," from 2010.

It's by no means the first time he's been shrunk either. The First Doctor and companions found themselves reduced to a tiny size by the TARDIS, in "Planet of the Giants," and a clone of the Fourth Doctor (and another of his companion Leela) was reduced to microscopic size and then injected into the Doctor's bloodstream in "The Invisible Enemy," so that they could fight off attacking antibodies.

There's a neat twist on a Star Trek theme, in that Rusty says "Resistance is futile"— a phrase more commonly associated with Star Trek's the Borg — but he's referring to life being irresistible, not their plans for military domination.

Director Ben Wheatley is perfectly placed as a Doctor Who director, given his track record in both horror and comedy, particularly the films Sightseers and A Field in England, which combine both elements to unsettling effect. Both of which star Michael Smiley, but Michael's involvement with Doctor Who actually precedes the Russell T Davies revival, as he starred as Seedleson in the audio drama "Creatures of Beauty" in 2003.

Danny Pink isn't the first soldier acquainted with the Doctor who retired from the forces to teach mathematics. According to events in the Fifth Doctor story "Mawdryn Undead," that's exactly what former Brigadier Alistair Gordon Lethbridge-Stewart did when he left UNIT.

The Doctor says, "Mortuaries and larders, always the easiest to break out of" — a reference to the morgue in which he woke up after his seventh regeneration, in the 1996 Doctor Who TV movie.

Eagle-eyed fans noticed that there's a "Break the Silence" poster about school bullying in the supply cupboard of Coal Hill School that had previously appeared on the wall in Leadworth school, outside the headmaster's office, as Mels is being disciplined in "Let's Kill Hitler."

Although the Doctor's involvement with Coal Hill School is well established (it's featured in his first ever adventure, commonly known as "An Unearthly Child"), the Daleks also have also been there. In the Seventh Doctor story "Remembrance of the Daleks" the Doctor's old foes were found in the cellar, having built a transmat station down there. And fittingly, Coal Hill was where they learned to fly, or at least the stairwell of the school was the first place we'd seem Daleks levitate up the stairs.

An iconic item of sonic architecture from this episode is the Dalek heartbeat, which comes from their very first appearance in 1964. It's a common feature of Dalek stories, including "Evil of the Daleks," a thematically similar story in which the Second Doctor manages to convert some Daleks to the cause for good, causing civil unrest in their ranks and eventually winning the day.

If you're thinking of joining any kind of futuristic space army, and your name is Ross, try and keep away from the Doctor. The UNIT soldier who dies at the hands of the Sontarans in "The Poison Sky" is called Ross, and in this story Ross is the name of the soldier who dies first. And we never see him meet Missy at the end either. Speaking of which, the scene at the end in which Missy meets Gretchen was directed by Rachel Talalay, as Ben Wheatley wasn't available.

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