Doctor Who: Knock Knock geeky spots and Easter eggs

Doctor Who series 10 strikes gold with Knock Knock - and there were some interesting references in it, too...

This article contains lots of spoilers for Doctor Who.

Knock, Knock is a real treat – a spooky, atmospheric tale with an emotional core and some brilliant guest performances. And in a sense it’s a real treat for this writer too, as it’s one of those Doctor Who episodes that’s so fresh and unlike anything the series has done before in its 54-year history (intentionally or otherwise) that this article is significantly shorter than usual; we hope that’s okay. But as ever, if you think you’ve spotted something we’ve missed, please do leave it in the comments below…

Poirot’s Last Case

We’ll start with a reference that wasn’t – in this month’s Doctor Who Magazine, the episode’s writer Mike Bartlett revealed that Bill’s friend Harry is actually the grandson of Harry Sullivan, companion to the fourth Doctor from 1974 to 1975. Sadly, Harry Sullivan wasn’t the grandfather who tried to steal a piece of the Great Wall of China with his boyfriend, and the Powers That Be decided that ‘in 2017, people might not remember one companion from 40-odd years ago, so it got cut.’

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The Landlord is played by accomplished stage and screen actor David Suchet, who is best known to the British public for his portrayal of Agatha Christie’s detective Hercule Poirot, whom Suchet played in 70 episodes from 1989 to 2013. Christie herself, of course (well, a fictional version played by Fenella Woolgar), met the tenth Doctor in 2008’s The Unicorn And The Wasp.

The Doctor reveals to Bill that he’s a Time Lord, a fact that wasn’t fully established on screen until 1969’s The War Games – though the Doctor had met another member of his species, the Meddling Monk, in 1965’s The Time Meddler and The Daleks’ Master Plan. In The War Games, their robes were rather simple and understated; by 1972’s The Three Doctors they were becoming larger and more colourful, but it wasn’t until 1976’s The Deadly Assassin that their famous big collars were introduced to an unsuspecting world. Time Lords don’t always wear them, though – they’re intended as ceremonial garb.

‘Sleep is for tortoises’ was a line spoken by the fourth Doctor in 1977’s The Talons Of Weng-Chiang. The third, fifth, seventh, eighth, tenth and twelfth Doctors all spent significant periods of time unconscious following their regenerations, while the second Doctor has a big sleep in The Two Doctors following a very big lunch in Seville – though he was undergoing a transformation into an Androgum at the time.

The Doctor does sleep at other times, though; we first saw him having a nap during 1965’s The Rescue. In 2015’s Sleep No More he tells Clara that he sleeps when she’s not looking – something which she should already have known, given that the Doctor revealed in 2013’s The Day Of The Doctor he and Clara had conversations about his dreams of home. However, the Doctor definitely doesn’t need as much sleep as his companions; 2011’s Night And The Doctor minisodes revealed that the eleventh Doctor regularly had adventures with River Song while her parents Rory and Amy were fast asleep…

Regeneration is, of course, the mechanic by which the show’s lead actor has been allowed to change ever since 1966’s The Tenth Planet. This almost wasn’t the case, however; in that year’s The Celestial Toymaker, an ailing William Hartnell is rendered invisible and mute for most of the story by the godlike titular antagonist. Producer Innes Lloyd had wanted to then bring in a new actor when the Doctor was restored – but the idea was vetoed.

It is perhaps worth noting the twelfth Doctor’s reaction to the regeneration question – does he know something the audience doesn’t? There’s a precedent for the Doctor knowing his end is near: the fourth Doctor had visions of the ghost-like Watcher, while the tenth Doctor received a warning about his own, first from the Ood in Planet Of The Ood and then from Carmen in Planet Of The Dead. The eleventh Doctor knew he would die on Trenzalore, having previously visited it in 2012’s The Name Of The Doctor.

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It’s even possible, if unlikely, that his regeneration has already begun; the tenth Doctor staved off his regeneration in 2010’s The End Of Time to embark on a farewell tour in which he revisited several of his old companions, and it was later revealed in the Sarah Jane Adventures episode The Death Of The Doctor that the tenth Doctor revisited all of his past companions on this trip.

The Doctor’s magic index finger makes another appearance, having last been used to detect the year in 2015’s Before The Flood. The seventh Doctor previously used it to determine wind direction in 1989’s Battlefield, but other uses have included working out which of Delta Magna’s moons the fourth Doctor was on in 1978’s The Power Of Kroll and locating the flight deck in 2010’s Flesh And Stone.

Bill tries to channel her inner Indiana Jones by looking for the switch to a secret passage within a bookcase. However, this never happened in any of the Indiana Jones films – it was a revolving fireplace that transported Indy and his dad in Indiana Jones And The Last Crusade. The popular trope has previously appeared in Doctor Who, though – Sarah Jane Smith pulled a book to reveal a passage to an alien spacecraft in 1975’s Terror Of The Zygons.

Wooden Acting

This isn’t the first time the Doctor has encountered beings made of wood; the ninth Doctor befriended Jabe, a tree from the forest of Cheem, in 2005’s The End Of The World, while the eleventh Doctor faced the Wooden King and Queen, embodiments of the sentient trees of Androzani, in 2011’s The Doctor, The Widow And The Wardrobe.

Bill’s friends should be careful when speculating about little dolls that have come to life – the gruesome plastic Troll Doll embedded itself in the throat of one of the Master’s opponents (and in the nightmares of a nation’s children) in 1971’s Terror Of The Autons, while the eleventh Doctor faced deadly living wooden dolls in 2011’s Night Terrors.

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The Doctor’s companions leading separate lives and having ‘bits that he’s not in’ is a phenomenon which really only began in 2012, when Amy and Rory started travelling with the eleventh Doctor again, having left him so they could settle down together the previous year. The Doctor then popped in and out of their lives – including the episode The Power Of Three, in which the eleventh Doctor was seen indulging his liking for Chinese food with the pair. The next companion had a similarly detached life; the 2014 series saw her holding down both a regular teaching job and a steady boyfriend between excursions.

Once again our hero suggests that he can help because he’s a doctor, but though he seems to have a good knowledge of the human body his medical qualifications have never been established; in 1967’s The Moonbase, the second Doctor tells companion Polly that he obtained a medical degree in Glasgow in 1888, while the third Doctor tells Liz Shaw that he’s a doctor of ‘practically everything’. However, the first and fourth Doctors both claimed on a few occasions to not be qualified physicians, so we’ll probably never know the truth.

So who, or what, is in the vault? The obvious choices would be the Master or Missy, but Steven Moffat doesn’t always go for the obvious. Given the Doctor’s regeneration anxiety, could it be the next Doctor in the vault? It’ll be an incredible surprise if it is, but since Steven Moffat has already said Chris Chibnall will be writing the new Doctor’s words (As Moffat himself did for the eleventh Doctor at the end of The End Of Time) it seems unlikely.

A senior Den of Geek writer who shall remain nameless (okay, it’s Simon) is convinced that the Doctor’s granddaughter Susan will in some way have an influence – backed up in this episode by Bill repeatedly referring to him as ‘grandfather’, the term Susan always used to address him – so could it even be her performing Beethoven’s Fur Elise behind those metal doors? Of course, it’s two other first Doctor companions who have previously been seen playing the piano on screen – both Steven Taylor and Dodo Chaplet tinkled the ivories at the Last Chance Saloon during 1966’s The Gunfighters. But then, Pop Goes The Weasel was previously sung by one of the giant spiders on Metebelis 3 during 1974’s Planet Of The Spiders, so could it be…?

No, probably not. But feel free to leave your own guesses in the comments below!

Pete is the co-writer and presenter of The Mostly Made-Up Doctor Who Episode Guide, a comedy podcast chronicling the Doctor’s adventures that is almost as well-researched as this article. You can find it on iTunes or at

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