[caption id="attachment_144376" align="aligncenter" width="1600"] The Magician's Apprentice (Photo: BBC)[/caption]

So, we're back. The Doctor has gone missing, Missy has returned from the dead to look for him too, and we've discovered an unpleasant truth about a mistake of compassion that he has only recently made, one that may make him culpable for a great many things, not least the end of his own race.

Before we find out the true, lasting significance of these events (in part 2, "The Witch's Familar), here are 10 things that also happened in "The Magician's Apprentice" that you may not already know the full significance of.

Naturally, there are a couple of spoilers in there, so watch the full episode here first:

The story begins on the foggy battlefields of Skaro, which we've previously seen parts of in the Fourth Doctor story "Genesis of the Daleks." At the time, it was noted that the soldiers had been at war for so long their supplies were a mix of old and new, and were seen carrying mixed up provisions—gas masks and radiation detectors—which has been echoed here in the bows and arrows, biplanes and blasters. The handmines are entirely new, however.

Missy's first declaration to UNIT, (once she has texted in her theme song) is "today I shall be talking to you through... the square window." This is a catchphrase from the British children's TV show Play School, in which the presenters would introduce a filmed item by offering a trip through one of three windows, square, round and arched. This isn't the first time he (or she) has been caught watching children's TV. He enjoyed the antics of The Clangers in "The Sea Devils," and discussed the physiognomy of Teletubbies in "The Sound of Drums."

When the Doctor spots Clara and Missy in the auditorium in which he has introduced a tank and an electric guitar. The riff he plays is "Oh, Pretty Woman" by Roy Orbison.

This isn't the first time the Doctor has been without his trusty sonic screwdriver. After it was first introduced during the era of the Second Doctor, the sonic lasted until the Fifth Doctor's time, when it was destroyed by Terileptils (in "The Visitation"). It didn't return until the Eighth Doctor pulled it out in the 1996 TV movie, was visible in "The Night of the Doctor", and the War Doctor had his own in "The Day of the Doctor" (to put things in their proper order in the Doctor's timeline). From the Ninth Doctor onwards, it has never been far from his grasp.

The Doctor's instance on playing loud heavy metal guitar and teaching people from the past to use the word "dude" has affectionate echoes of the movies Bill & Ted's Excellent Adventure and Bill & Ted's Bogus Journey, in which two Californian hard rockin' teenagers round up characters from history in order to help them with their homework. Their method of travel is a phone box, so it's safe to say the feeling is mutual.

Missy describes the TARDIS as being "the dog's unmentionables," which is a sanitized version of the British slang phrase "the dog's bollocks." There's a thorough roundup of the origins and alternative uses of the expression here, but suffice to say, it's highly complimentary.

During the section where Davros is discussing the past with the Doctor, there are selections from their previous confrontations, including the Fourth Doctor's first meeting with him in "Genesis of the Daleks," and the memorable phrase "unlimited rice pudding," the Seventh Doctor's sarcastic riposte to Davros's endless hunger for power in "Remembrance of the Daleks":

https://www.youtube.com/watch?v=IJ-zt-o2mIM

(Oh, and if you've not met Davros before, here's his Rogue's Gallery entry‘Doctor Who’ Rogues Gallery: Davros).

"And three possible versions of Atlantis" might sound fanciful, but the legendary lost empire has appeared in Doctor Who three times. The Second Doctor visited the underwater kingdom in "The Underwater Menace," while the Third Doctor (and the Master) was part of the chain of events that destroyed it in "The Time Monster." There was also a passing reference in "The Daemons," as discussed here.

With regard to Missy's claim that she and the Doctor are best friends, there's a persistent rumor that the Master was originally intended to be revealed as the Doctor's brother. Roger Delgado, the First Master, died before the story could be filmed, and even his successor Anthony Ainley had a moment with the Fifth Doctor in "Planet of Fire" when he begged "won't you even show mercy to your own..." before being overcome by gas.

NEXT: 10 Things You May Not Know About ‘The Witch’s Familiar’

Now go back and read the entire 10 Things You May Not Know About Doctor Who archive.