Heaven Sent (TV story)

Heaven Sent was the eleventh and penultimate episode of series 9 of Doctor Who.

The episode shows the Doctor dealing with and grieving over the death of Clara Oswald, whom he lost to the Quantum Shade in the previous episode. The vast majority of the episode includes just the Doctor by himself with no other characters present, save the veiled figure that menaces him throughout. Jenna Coleman appears only as a manifestation of Clara in the Doctor's imagination. The Doctor's TARDIS is also absent from this episode, except again in the Doctor's imagination.

The episode is notable for a number of truths conceded by the Doctor, with him being inside his own confession dial. It is also notable for showing the Doctor finally finding his way back to Gallifrey since he found out that it was not in fact destroyed in the Time War, but instead placed in a pocket universe.

This story takes place over an outstandingly long period of time, seeing the Doctor stuck in a recursive cycle during which he repeatedly perishes and comes back to life. In the following episode, Hell Bent, it is estimated that this cycle lasts for four and a half billion years, leaving it with one of the single-longest uninterrupted time spans of any given adventure in Doctor Who history.

Synopsis
As if the death of his best friend wasn't enough, the Doctor's situation has only gotten worse. What initially started as an attempt to help clear someone of a false murder charge has evolved into to something much worse.

Now trapped in an old rusty castle in the middle of an ocean, the Time Lord is being stalked by a mysterious creature that only pauses when he gives up his deepest secrets. What does this thing want? And can the Doctor escape and find his way back home?

Plot
As gears turn inside the walls of a castle, a mysterious figure, with blood on his hands, makes his way into a room with a teleporter. He flips a switch and collapses to the ground, his body fading away into dust, as the teleporter activates, materialising the Doctor inside its chamber. The Doctor steps out of the teleporter, looking around the room. He bends down to grasp some of the sand on the ground, the memory of Clara's death still fresh in his mind. He then threatens the ones responsible for bringing him there, promising to never stop until he finds them.

The Doctor steps out of the teleporter room and into a circular corridor, filled with windows and a monitor. Looking out one of the windows, he sees that he's inside the central tower of a castle. He speaks out to whoever captured him, again, mentioning that the technology in the teleporter means he can only have been moved a maximum of one light year from where he was before, and he knows that he hasn't travelled in time, so all he has to do is wait until nightfall, and then he'll be able to use the stars to figure out where he is.

Walking down the corridor, he finds a spade, covered in dirt, leaning against one of the walls. He starts shouting again, trying to get the kidnappers to come out and face him. At that moment, the monitor in the corridor activates, showing the Doctor himself on the screen. Seeing that the image is being projected from something outside one of the windows, the Doctor runs over to said window and looks outside. He sees a hooded figure in another window, looking right at him. It is from this figure that the footage on the monitor is coming from. The Doctor backs away from the window in fright, watching as the figure turns and moves away.

Looking at the monitor, the Doctor watches as the image moves down a corridor. The Doctor finds the particular corridor, and sure enough, the figure is coming towards him. The Doctor runs down another corridor to a door but finds the door locked. He turns back in time to see the figure enter the hallway and realises he's seen this creature before. He turns back to the door and uses an old trick he knew when he was younger, to form a psychic link with the door, getting it to unlock.

He opens the door, only to find a wall. He turns back to see the figure coming closer and closer to him. Unfortunately, he can't see a way out of this situation. As the figure reaches for him, the Doctor admits that he is scared of dying, and the figure freezes. The Doctor wonders if this is because of something he said. He notices that even the flies that were buzzing around the figure have also frozen in place.

A noise causes him to step over to the window. He watches as the sections of the castle begin to revolve, rearranging themselves. He turns back to the door to see the wall slide open. Running through the new opening, the Doctor finds himself in a bedroom.

The Doctor grabs one of the flowers but freezes when he notices a portrait of Clara sitting on top of the fireplace. He smiles sadly at the picture, before grabbing a miniature magnifying glass, so he can take a closer look, not noticing the nearby monitor. The monitor is showing that the figure is on the move again, and is entering the bedroom.

The Doctor deduces that the painting is very, very old, before noticing a fly on it. He quickly turns and sees the figure. He talks about a time when he was a child. He had seen a dead, old woman, who was covered in veils. It was a hot day, so flies were buzzing around her corpse. The sight of this gave the Doctor nightmares for years. He recognises the figure as that very nightmare...

As he tries to question the Veil, he pulls out petals of the flower, letting them drop to the ground. Avoiding letting the Veil touch him, the Doctor deduces that the castle is some type of torture chamber, to get information out of him; whoever did this picked the thing he feared most out of his mind and gave him a tailor-made hell. The Doctor refuses to play along and runs over to grab a stool, throwing it through a window. "I told you I was scared of dying, and I wasn't lying. Advantage me!" He then jumps through the window himself, falling down towards the misty depths below.

The Doctor walks into the TARDIS, apologising for being late. He says it's because of jumping through the window and asks if he should reveal how he got out of that situation alive. He turns to look at Clara, who is standing near a chalkboard, with her back to him. On the TARDIS monitors, the Doctor can see the fall, revealing that he isn't really in the TARDIS with Clara. He is actually still falling but has sped up his thinking process to slow down his perception of time. The TARDIS that he is standing in is a "storeroom" within his own mind, which he has created to give himself more time to think.

The Doctor reveals he had smelled the salty air earlier, which means the castle is standing in the sea. But jumping from a great height into the water doesn't guarantee that he will survive, so he needed to know the exact distance between the window and the water, which is why he threw the stool through the window. He listened for the splash of the stool reaching the water, which took seven seconds. Other things he had done in the room, including dropping the magnifying glass and the flower petals, were to determine other factors that he used to determine if he could survive the fall. "Rule One about being interrogated: you are the only irreplaceable person in the room. If they threaten you with death, show 'em who's boss. Die faster."

The Doctor successfully dives into the water, but falls unconscious, represented in the mind TARDIS by everything turning off. The lights start turning back on and the mental manifestation of the Doctor wakes up to the sound of Clara writing on the chalkboard. He looks at the chalkboard to see what is written: Question 1 - "What is this place?" The Doctor asks why he can't just sleep. On another chalkboard, Question 2: "What did you say that made the creature stop?" The Doctor asks if he has to know everything. On a third chalkboard, Question 3: "How are you going to WIN ?"

At that moment, the Doctor fully regains consciousness in the water. As he floats in the water, the Doctor makes a horrifying discovery; On the seabed are many skulls. He quickly swims back to the surface, ending up at the base of the central tower. The Doctor walks inside and into a room with a lit fireplace. Warming his hands with the fire, the Doctor discovers an identical set of his clothes next to the fireplace. The Doctor takes the duplicate clothes and trades them with his own, making sure to place his clothes exactly as the other set were placed, before leaving the room.

The Doctor finds a small room, with arrows pointing to a missing section of the stone floor. He looks up at the nearby monitor, noting that the Veil keeps coming for him. He asks why it does that. In the mental TARDIS, Clara writes on a chalkboard again: "Wrong question!" Upon asking her what the right question is, he gets a written response: "Not why. What?"

The Doctor walks over to the monitor, pondering on the fact the Veil is tracking him. He realises that the Veil is trying to terrify him, as the monitors are set to show him where it is at all times. The castle and the Veil are a killer puzzle box designed to scare him to death. Smirking, the Doctor comments that it must be Christmas - this is exactly something that would be on his list.

The Doctor heads down another corridor that leads him to an outside garden. He notices a rectangular mound of dirt in the centre of the garden, and a spade nearby, which means something is buried beneath the mound that he is supposed to dig up. Grabbing the spade, the Doctor contemplates whether to start digging, as it could be a trap or a clue left by a previous prisoner. After all, the presence of the skulls proves that there were others here before the Doctor. Noting how slow the Veil is moving, the Doctor deduces he has an hour before it arrives, so he starts digging.

Sometime later, the Doctor is still digging, having not found whatever is buried, when he notices flies buzzing near him. Running to the nearby monitor he sees that the Veil is strangely standing in one place, staring at a smooth surface. The Doctor opens the door to leave the garden, only to discover the Veil standing on the other side. The Veil quickly tries to enter the garden, but the Doctor manages the force the door shut, and props the spade against the door in a way to keep it shut. The Veil continues to try to force the door open a few more times, before walking away. The Doctor looks at the monitor and notes that the Veil has walked into the room with the missing section of the floor. Wondering where it's going, the Doctor looks around. The door is the only way in or out of the garden. "Well, since you're going.." he mumbles and grabs the spade, resuming his dig.

Hours later, when night has fallen, the Doctor stops digging and looks up at the stars. He frowns in confusion, noting something wrong with them, before resuming his digging. His spade hits something. Digging with his hands, the Doctor uncovers the missing section of the floor from the other room. On it, words are written: I AM IN 12. At that moment, the Veil emerges from the ground nearby, having dug its way from the room to the garden.

The Doctor walks into his mental TARDIS again, thinking about how he is going to get out of this situation. He tells Clara to ask him a question and she writes something on the chalkboard: "Tell no lies." She then rewrites question two again. The Doctor did note that it was when he admitted to being scared to die, that the Veil stopped. But, it's not just the truth that the Doctor's captors are trying to get out of him. They want his confessions, the secrets he never tells anyone. The problem is that there are truths the Doctor can never tell, not for anything. But now he is scared and alone.

Back in the real world, the Doctor confesses that he didn't leave Gallifrey all those years ago because he was bored, but because he was scared. The Veil backs off and the castle shifts again. The Doctor quickly climbs out of the hole and escapes from the garden. The Doctor then makes another discovery. The castle is standing in the sea, alone, with no other land anywhere nearby.

As time goes on, the Doctor uses his hand to tap out the seconds it takes for the Veil to walk from one side of the castle to the other, where he is, in order to work out how much extra time he can get before the Veil shows up again. He can get 82 minutes to himself if he leaves the Veil in one extreme end of the castle when he runs to the other extreme. Having some soup at one point, the Doctor wonders if the teleportation sent him to Hell; he shrugs off the idea "That's okay. Hell's just Heaven for bad people." During this, he is trying to locate Room 12, having noticed that the rooms are numbered, but due to the castle rearranging itself, the rooms are not in the correct order. He has also noticed that most rooms after he has left them for a while, reset to the condition they were in before the Doctor arrived.

The Doctor returns to the teleporter room and looks at the nearby console. He then notices that two cords of the console are attached to a nearby skull. Detaching the skull, the Doctor notices that its owner had written one word in the sand before he died: 'BIRD'. The Doctor wonders what it could mean (even asking if there are birds here), as he watches the word disappear from the ground.

A wall nearby slides open, leading to a staircase. The Doctor uses the staircase, emerging at the roof of the tower. Setting the skull on a ledge, the Doctor looks around, knowing he is missing something. Earlier, he had located Room 12, but found a wall behind the door, meaning he has to give another confession to access the room. The Doctor knows that the room is a trap of some kind. This whole thing is someone's game that the Doctor can't stop playing, a game that everyone who came before him has lost.

Looking up at the stars again, the Doctor asks what is wrong with them. They are all in the wrong place for this particular time zone. If he didn't know better, he would say that he has somehow travelled 7,000 years into the future, but he knows for a fact that he hasn't time travelled.

As he ponders this, the Veil arrives, but before it can grab the Doctor, he mentions the Hybrid. Turning to face the Veil, the Doctor talks about the Hybrid. Long before the Time War, the Time Lords knew the War was coming. There were many prophecies and stories concerning it. One of the prophecies mentioned a creature called the Hybrid, who was half Dalek and half Time Lord, the ultimate warrior. The Doctor confesses that he knows that the Hybrid is real, that he knows where it is, and what it is. He confesses that he is afraid of it. The Veil backs off and the castle shifts again. When it does so, the skull falls from the ledge and into the water, joining all the other skulls already on the bottom of the sea.

The Doctor quickly runs back to Room 12, to find that the wall has slid away, revealing a long hallway. Walking down it, the Doctor finds a room, with a semi-transparent wall, with the word "Home" written on it. The Doctor realises that this is the final obstacle. He believes that the TARDIS is on the other side of this wall, one confession away from him. Using the sonic sunglasses, the Doctor determines that the wall is made out of Azbantium, a mineral four hundred times tougher than diamond. He also determines the wall is twenty feet thick. He then thinks back to the word "BIRD", and that's when his memory snaps back into place.

The Doctor walks into the mental TARDIS, ranting over what he has remembered and what he must do. He tells Clara that he can't keep doing this. Clara writes question three again. The Doctor asks if he can just lose. It would be easy. All he would have to do would be to confess the secret details of the Hybrid. Asking Clara again, why he can't lose, he sees that she has written something new: "No!"

The Doctor tells her that he remembers everything and that she doesn't understand. He can remember it all, every time, and she'll still be gone. The Doctor collapses onto a stair, finally letting out his grief over Clara's death. Suddenly, Clara is facing him and talking to him. She tells him that he is not the only person who has ever lost someone. It's the story of everybody. She tells him to get over it, to beat it, to break free. She tells him it's time to move on. She tells him to get up and win.

In the real world, the Doctor stands back up, seeing that the Veil has reached the hallway and is walking towards him. He apologises to it, saying he has no confessions left for it, but he will tell it the truth. Turning back to the Azbantium wall, the Doctor starts punching it, while revealing that the Hybrid is a very dangerous secret that needs to be kept. So, instead of confessing the secret, he will instead get out of here and find the ones responsible for putting him in here. As he continues to punch the wall, he decides to tell the Veil a story from the Brothers Grimm. He continues to do so until the Veil finally reaches him and grabs him, severely burning him. As the Doctor collapses to the ground, the Veil steps back and vanishes.

Inside the mental TARDIS, the Doctor says that Time Lords take forever to die, even when they are too injured to regenerate; their bodies will try using all its regeneration energy to save them. As he says that, in the real world, he starts moving again, crawling out of the room. As the Doctor makes his way back to the teleporter room, he reveals everything he remembered. The castle was created specifically for him. There were no prisoners before him. The stars weren't in the wrong places and the Doctor didn't time travel. He's just been here a very, very long time.

The Doctor reaches the teleporter room and stumbles over to the control panel. Since most of the rooms reset to their original condition, it's logical to assume that the teleporter room has also done so. As such, inside the teleporter's hard drive is a copy of the Doctor, as he was when he originally arrived... 7,000 years ago.

All he has to do is add energy to the teleporter to activate it, and the only energy source he has is himself. Hooking up the two cords to his head, the Doctor pulls the switch. Collapsing to the ground, the Doctor only has enough time to write the word "BIRD" in the sand.

Before he dies, he asks "How long can I keep doing this, Clara? Burning the old me... to make a new one?"

After that, the mental TARDIS lights shut off and his real body fades into oblivion, leaving nothing but his skull.

At that moment, the teleporter activates, materialising the new Doctor in the chamber, exactly as he was when he first arrived, including the state of his memories, continuing the cycle he has been in for the last 7,000 years, down to what he says in the same tone as he warns whoever brought him there that they will pay for Clara's death.

The Doctor continues to repeat everything over and over again, each time getting further into the Azbantium wall; he gets a bit more of his story out as the centuries pass. Each time, he is encouraged to continue trying to escape without revealing what he knew about the Hybrid; he continues to accept that he needs to keep fighting on to honour Clara's memory. Each time, he knows he has to keep fighting to find out who put him through this hell.

Over 4 billion years later, the Doctor is punching the Azbantium wall. Just as the Veil is about to touch him, the Doctor's last punch cracks the wall and reveals light. The last of the wall crumbles away, showing a white glow. Realizing the Veil hasn't killed him, the Doctor turns to see it fall apart, revealing it to be made of gears. Telling the mechanical creature his story is "a hell of a bird", the Doctor steps through the opening.

The Doctor exits onto a desert world, looking behind him to see the tunnel of Azbantium. In a flash, the opening closes and the item generating it drops to the ground. Picking it up, the Doctor discovers he had been trapped inside his confession dial the entire time. The castle and sea are then covered by a mass of gears and the cover of the dial comes back over it.

Just then, a boy runs up to him. The Doctor tells him to go to the city and tell someone important. "Tell them I'm back. Tell them I know what they did, and I'm on my way. And if they ask you who I am, tell them I came the long way around." The boy runs off towards the nearby city, revealing that the Doctor is now on Gallifrey.

The Doctor looks at the dial again and speaks to it. "You can probably still hear me. So, just between ourselves, you've got the prophecy wrong. The Hybrid is not half Dalek. Nothing is half Dalek. The Daleks would never allow that. The Hybrid, destined to conquer Gallifrey and stand in its ruins, is me."

Cast

 * The Doctor - Peter Capaldi
 * Clara - Jenna Coleman
 * The Veil - Jami Reid-Quarrell

The Doctor

 * The Doctor says he hates gardening.
 * The Doctor proves to be able to open a door by communicating with it, hinting he had more telepathic abilities when he was young.
 * The Doctor can feel time travel. Thanks to this, he can say he should be in the same time zone he left, but the position of the stars suggests otherwise.
 * The Veil is a creature pulled from the Doctor's childhood nightmares of an old lady who died and was covered up in veils and attracted flies due to it being a hot summer day.
 * The Doctor makes a "pop" sound with a finger in his mouth.

The Castle

 * A portrait of Clara Oswald is hanging in the castle.
 * When the Doctor finds 'BIRD' in the ground, he rhetorically asks if there are birds here.
 * The castle contains screens designed to show what the Veil sees, giving the Doctor clues as to where the Veil is at all times.
 * The Doctor is searching for Room 12.
 * The Doctor finds and generates billions of copies of his own skull.
 * The Doctor at first thinks the castle is inside a closed energy loop.

Culture from the real world

 * The Doctor discusses the Brothers Grimm to the Veil and the tale of the Shepherd's Boy, who is asked by the Emperor "how many seconds in eternity?" To this, he replies: "There's this mountain of pure diamond. It takes an hour to climb it, and an hour to go around it. Every hundred years, a little bird comes and sharpens its beak on the diamond mountain. And when the entire mountain is chiselled away, the first second of eternity will have passed." The Doctor thinks that's "a hell of a bird".

Technology

 * According to the Doctor, an "augmented ultra long-range teleport" brought him into the "castle".
 * The Doctor compares the teleporter to a 3D printer.

Story notes

 * Whilst the episode was promoted by various news outlets as a one-hander, the presence of an imagined Clara and the Veil, and the appearance of the young boy at the end of the episode, technically go against this; however, the bulk of the storyline was carried by the Doctor alone with him having all but one line of dialogue. The 2013 mini-episode Clara and the TARDIS remains the only true televised one-hander produced to date. The Companion Chronicle The Stealers from Saiph is the only other one-hander.
 * The Doctor's story that he tells in the beginning, is written on a wall in the old castle. Only certain parts are missing.
 * While imagining talking to Clara, the Doctor breaks the fourth wall, looks at the camera and says "I'm nothing without an audience".
 * The Doctor imagines he's in the TARDIS with Clara, who writes responses on the blackboards, whenever he needs to think about a scenario. This is quite similar to the "mind palace" from Sherlock, a show created and written by Steven Moffat and Mark Gatiss; Sherlock would review facts and even talk to mental constructs of people he knows when working out a case/problem.
 * In the TV special The Ultimate Time Lord, Steven Moffat had described the Doctor as "an adrenaline junkie. He will toss himself out a window and figure out what to do on the way down." The Doctor does this very thing in the episode.
 * Each and every one of the skulls in the episode were modelled from Peter Capaldi's own skull.
 * Jenna Coleman's name has been removed from the opening credits, making this the first regular episode of the revived series to only credit one actor during the title sequence. To make up for the extra time required, Capaldi's name is held on screen for a couple of seconds before moving away, also a first. In keeping with this, in the closing credits, the name of the actor playing the Doctor is seen on screen by itself for the first time, with the companion actress' credit moved to the second screen.
 * Unusually for the title sequence used beginning in 2014, Peter Capaldi's credit zooms ahead rather than fading out.
 * Prior to the broadcast of Series 8, Steven Moffat stated in interviews that he had already worked out the cliffhanger for the penultimate episode of Series 9, and was quoted as saying "you won't see it coming." The Doctor says almost those exact same words before jumping out the window in this episode, the penultimate episode of Series 9 which does, indeed, lead to a major cliffhanger.
 * This marks the only penultimate episode in a series during Steven Moffat's era as showrunner to not feature the Cybermen, though as there are only twelve episodes in this series, the following episode continues the pattern of the twelfth episode featuring Cybermen.
 * Writing in DWM 495, Moffat confirmed that the portrait of Clara was painted by the Doctor himself. He also implied that several other clues, specifically the "I am in 12" paving slab, were left by a previous copy of the Doctor who was impatient with the duration of each cycle, while leaving it up to the viewer to decide for certain.
 * The only appearance of the TARDIS in this episode is an imaginary version of the console room in the Doctor's mind.
 * In the original script, available to download from the BBC Writers Room website, the last word of the Doctor's final line is capitalised as a proper noun - "The Hybrid, destined to conquer Gallifrey and stand in its ruins, is Me." This less ambiguously points to Ashildr and her appearance in the following episode, where the Doctor confirms that he believes her to be the Hybrid.
 * This story can be read as an elaborate metaphor for battling one’s own depression. In an interview, Moffat confirmed that this was not intentional, but stated he was ‘honoured’ that it had helped out people in dark places.

Ratings

 * BBC One Overnight: 4.51 million
 * BBC America Overnight: to be added
 * Final UK ratings: 6.19 million

Filming location
to be added

Production errors

 * In one of the shots of the Doctor punching the azbantium wall in the montage spanning over 4.5 billion years, the Veil is at least three metres behind him, yet the shot is then shown from the side, and the Veil is directly behind him.
 * In all of the scenes where the Doctor states how many years he thinks he's traveled, the green screen for the stars seems to go through the Veil's hand and face.
 * The same error is present on the Doctor's on face in the version where he says "two billion years" - the parts of Peter Capaldi's face that are in shadow have been erroneously painted out by the green screen effect.
 * In the montage of the time loop, when the Doctor refers to how many years into the future he has traveled, the stars in the background are always in the same configuration and positions.
 * When the Doctor drops his spoon during his eating a soup, another spoon can be seen at that same place Capaldi had his before it dropped, only it seems to be behind his own hand. The spoon that remains is still, not moving with the rest of the frame, suggesting that this was a composite of two shots - one of the spoon dripping, and another of the spoon being dropped, with the dripping spoon not having been removed.
 * When the Doctor jumps from the window into the water, he passes through a section of the castle on the way down.
 * When getting out of the water the Doctor's suit and skin is visibly dry and his hair only moisturised.
 * The stars barely change from the top of the tower between the scenes at 1,000,000,000)] years and [[2000000000_(number)|2,000,000,000 years. In a billion years, stars would have moved, new stars would have been born and some some would have become red giants or died.

Continuity

 * The Doctor declares to his captors, "the Doctor will see you now". (TV: The Eleventh Hour)
 * The Doctor remembers Clara's death and how she told him not to take revenge, as well as telling the reason she got killed; he also refers to the fact she died in agony. (TV: Face the Raven)
 * The Doctor refers to a skull which he finds as his "predecessor," not knowing how correct he is in that reference. had previously referred to a skeleton in the Death Zone on Gallifrey in the same way. (TV: The Five Doctors)
 * The Doctor retreats into an imaginary version of the TARDIS. (AUDIO: The Pyramid of Sutekh)
 * The Doctor says people should know better than to trap him. The Eleventh Doctor warned the Weeping Angels about the same. (TV: The Time of Angels)
 * The Doctor retreats to the lower level of the mental recreation of the TARDIS console room when he becomes emotional, and sits in almost exactly the same place as the Eleventh Doctor did when faced with an enforced journey to Trenzalore. (TV: The Name of the Doctor)
 * The Doctor says to always assume survival. Clara previously said he always assumes that. (TV: The Witch's Familiar)
 * Except for the painting, all of the Doctor's visions of Clara have her wearing the same outfit and hairstyle as when she died. Also, except for one encounter, she is always seen from the back, which is how the Doctor last saw her alive. (TV: Face the Raven)
 * The Doctor is once again able to recgonise the artificial nature of the events he is caught up in. (TV: Sleep No More)
 * The Ninth Doctor demonstrated the ability to slow down his perception of time when carrying out a risky action. (TV: The End of the World)
 * The Hybrid is discussed. (TV: The Witch's Familiar)
 * The Doctor says the Daleks would never allow anything to be half-Dalek. He has previously witnessed them destroy human-Dalek hybrids (TV: Evolution of the Daleks) and has encountered a race of Daleks harvested from human genetic material who were driven insane by their own existence. (TV: The Parting of the Ways) A hybridisation of a faction of Daleks has also more than once been the cause of civil war. (TV: The Evil of the Daleks, Revelation of the Daleks, Remembrance of the Daleks)
 * The Doctor returns to Gallifrey, having got there "the long way round". (TV: The Day of the Doctor)
 * The Doctor previously had a connection to a room with his incarnation's number. (TV: The God Complex)
 * The Doctor jokes about being "good at traps". (TV: The Time of Angels)
 * The Doctor says "it must be Christmas" when faced with a challenge. (TV: The Vampires of Venice) He has also referred to anachronisms and puzzles being on his Christmas list before. (TV: A Town Called Mercy)
 * The Fourth Doctor encountered a recursive environment inhabited by numerous previous iterations of its occupants with his companion Adric. (PROSE: Mauritz)
 * Clara challenges the Doctor to win. (TV: The Girl Who Died)

DVD releases

 * Doctor Who Series 9: Part 2
 * Doctor Who: The Complete Ninth Series

Blu-ray releases

 * Doctor Who Series 9: Part 2
 * Doctor Who: The Complete Ninth Series