Let's Kill Hitler (TV story)

Let's Kill Hitler was the eighth episode of series 6 of Doctor Who. It was written by Steven Moffat, directed by Richard Senior and featured Matt Smith as the Eleventh Doctor, Karen Gillan as Amy Pond and Arthur Darvill as Rory Williams.

It was the first episode in the autumn half of the sixth series. It was, in a sense, the second episode of a two-part story, preceded by A Good Man Goes to War. Like A Good Man Goes to War, it revealed much about River Song's origins, also dealing with Amy and Rory's childhood and how they became a couple. Additionally, it explained why the Silence had been trying to kill the Doctor and it is stated that the Doctor's death at Lake Silencio is a fixed point in time. At the end of the episode and in following episodes, the Doctor is occasionally seen looking at the information he downloaded from the Teselecta on his death.

The episode featured the first "Time Lord-style" regeneration of a female that showed the complete change in physical appearance from old to new incarnation on-screen. Previously, such regenerations were shown with the change from an old form already completed or cut out before the physical change even began. Let's Kill Hitler also dealt with other aspects of regeneration, such as being able to rapidly heal from otherwise fatal injuries while the regenerative cycle was still in process, and a capability to donate some amount of regeneration energy to another at will.

This was the first televised Doctor Who story to feature the personal appearance of the tyrant dictator Adolf Hitler. However, although the title of this episode suggested the story might revolve around him, in truth he received close to five minutes of screen time and was quickly ejected from the plot. A few references to World War II and Nazism were present, but much of the episode focused on the first appearance of the Justice Department and the strange types of technology they utilised. Instead, the title comes from Mels' demand to be taken back in time to kill Hitler in the cornfield at the beginning.

In this episode, the shapeshifting robot known as the Teselecta is introduced. The Teselecta and her crew make a return in The Wedding of River Song where they play an important role in the plot. Unknown until the events of The Wedding of River Song, the Teselecta also appeared in the beginning of The Impossible Astronaut and played a major role there where the two episodes events were connected to each other.

Additionally, the episode introduces The Question which is described as "the oldest question in the universe, hidden in plain sight." While the Doctor learns of the Question from the Teselecta, he does not learn what it is or its significance to him. The Question is revisited in The Wedding of River Song where the Doctor learns what the Question is from Dorium Maldovar and why it means he must die and in The Time of the Doctor where the true nature of the Question and its meaning are revealed.

Synopsis
In the desperate search for Melody Pond, the TARDIS crash lands in Thirties Berlin, as the time-travelling drama returns for the second half of the series shown earlier in the year. The Doctor comes face to face with the greatest war criminal in the Universe. And Hitler. Old friendships are tested to their limits as the Doctor suffers the ultimate betrayal and learns a harsh lesson in the cruellest warfare of all. As precious time ebbs away, the Doctor must teach his adversaries that time travel has responsibilities. And he must succeed before an almighty price is paid.

Plot
Rory drives through a wheat field wildly as Amy gives directions badly. She is telling him how to trace letters by mowing down the wheat with the car that will spell out a name, trying to summon the Doctor in the loudest manner possible, so that he cannot avoid contact with them any longer by dodging Amy's phone calls. Stopping their car, they find the Doctor standing by his TARDIS in a new green pea coat.

He holds a newspaper with a photo of the crop circle reading "Doctor" they have just made, commenting "Seriously?" with an incredulous smirk on his face. Rory replies that the Doctor had not been answering his phone and this was the only way they could really get his attention. She asks if he has found Melody over the summer. The Doctor makes the bad news easier to deliver by asking Rory if he can give Amy a hug. Once he has permission, he embraces Amy and tells her "You know who she grows up to be, so you know I will find her." Amy notices that this is a polite of saying he failed to track down her baby. Rory examines the picture. There is a line in the message that they didn't make.

The trio suddenly learns what caused the unknown stroke in the message when they hear the high-powered engine of a sports car revving through the field and shredding a new line down the middle of their crop circle. All of them start screaming for their lives. They dodge out of the way as a Corvette almost runs them over. Out steps Amy and Rory's best friend, Mels, who flirts with the Doctor and fondles the TARDIS. With police sirens prophesying her arrest for car theft, she points a gun at the Doctor and demands he take her to kill Hitler.

Flashback: Mels is a childhood friend of Amy and Rory and a troublemaker at school. She gets in more trouble than anyone except boys, insults teachers, continually references the Doctor, steals buses and points out to Amy and Rory that they're in love. Back in the present, the TARDIS flies wildly because Mels has shot the time rotor. He barks at the delinquent, "You shot it! You shot my TARDIS! You shot the console!" Mels accusingly remarks, "It's your fault!" He inquires, "How is it my fault?" She replies, "You said guns didn't work in this place. You said we're in a state of temporal grace." Angry that she fired her gun out of foolish curiosity, he snarks, "Oh, that was a clever lie, you idiot! Anyone could tell that was a clever lie!"

In 1938 Berlin, a janitor watches a Nazi officer. In a futuristic control room, the crew discuss copying the officer as the janitor follows him. In the control room, a woman complains that the last time they relied on the computer, it "made Rasputin green". She goes to "the top level", where an electronic voice politely threatens her until she adjusts a device on her wrist. She looks through a view port, which is the eye of the janitor, actually a highly advanced ship, the Teselecta. She relays colour codes to the control room. The janitor becomes the officer's double and beams him aboard with a miniaturisation ray. Learning the officer's identity as a war criminal, the crew leave him to the antibodies. They politely threaten the officer before killing him.

The Teselecta enters Adolf Hitler's office while the captain complains about the shock-absorbers malfunctioning. Hitler asks why his officer has entered without permission. The Teselecta activates "justice mode" and paralyses him with a beam of light from its mouth. However, one of the crew says they arrived too early in his timeline, just before the TARDIS crashes through a window and knocks over the Teselecta.

The TARDIS occupants stagger out in a cloud of smoke caused by Mels' havoc. Hitler thanks the dumbfounded travellers for saving him and asks what the TARDIS is. The Doctor advances on him, saying it's a police box and "The British are coming!" The Teselecta picks itself up and a panicky Hitler fires at it. Rory punches out Hitler and takes his gun.

The Doctor and Amy help up the Teselecta. Rory shoves Hitler in the cupboard while the Teselecta goes into observation mode — "fainting". Mels staggers forward. She calls Hitler a lousy shot and collapses; she was hit by a bullet. Rory tries to help her and the Doctor tries keeping her conscious by talking to her. Mels says she wanted to marry the Doctor and he promises to ask her parents when they fix her up. Mels says they're right there, then begins to glow. The Doctor, who recognises that Mels is starting to regenerate, pulls the others away from her.

Mels comments about regenerating once before as a child in New York and reveals her actual name to be Melody. Amy says she named her daughter after her, but the Doctor explains, "You named your daughter after your daughter" and Mels finally regenerates with a scream.

The crew of the Teselecta look in bewilderment at a criminal whose crimes dwarf Hitler's: Melody Pond. Melody ends her regeneration in her River Song incarnation. She chatters on about her new look before going off to weigh herself.

The three time travellers talk, realising that Melody is River Song right at the beginning. Melody asks who River is, but the Doctor refuses to tell her "spoilers". She pulls out a gun, "getting back to business", points it at the Doctor and pulls the trigger. The gun, emptied by the Doctor during the regeneration, clicks uselessly. A scintillating conversation ensues and Melody pulls a banana at the Doctor, who had turned the fruit bowl she had left the gun in, then Melody swings a letter opener at him but is disarmed. The Doctor asks why she didn't kill him in the field and receives the reply that they'd only just met — she's a psychopath, not rude.

An impatient Melody asks if killing him will take all day. The Doctor inquires if she was busy and, an explanation that the Silence tailored Melody as the Doctor's "own bespoke psychopath" later, Melody kisses him with poisoned lipstick and jumps out a window to go shopping. The Doctor gives Amy his sonic screwdriver and tells her to find Melody. Dying, he stumbles into the TARDIS.

Outside, Melody enrages soldiers into shooting her. Rory, horrified, cries out, "No!" as his daughter is pelted by automatic gunfire. However, she is within the first fifteen hours of her regeneration; she produces a shock wave that heals her and knocks out the guards. She steals a motorcycle. Amy and Rory steal another and follow her.

Inside the TARDIS, the Doctor turns on the voice interface as a hologram of himself. He asks for someone he likes. In succession, it offers images of Rose Tyler, Martha Jones and Donna Noble, all of whom induce wails of guilt. Finally, it offers young Amelia Pond, who tells the Doctor that he will shortly be dead. The poison comes from the Judas tree, and regeneration is not available. The Doctor tries to get "Amelia" to help him gather his strength. It insists it is not Amelia, but a hologram. He collapses, gasping for help, then hears Amelia the hologram say "Fish fingers and custard". He finds the strength to drag himself to the console.

Elsewhere, Melody enters a restaurant and orders the patrons at gunpoint to take off their clothes. Outside, Amy and Rory wonder where she is. They see the screaming restaurant patrons run out in their undergarments and hurry in just as the Teselecta, now in Amy's form, arrives.

Melody is working on her ensemble when Amy — actually the Teselecta — runs in. Amy and Rory wake up where the Nazi officer did. They are threatened politely by the antibodies until a crew member gives wrist devices to ward them off. They are taken to the bridge, where they are told that their memories of these events will be erased later.

Outside, the Teselecta asks Melody why she killed the Doctor on behalf of the Silence. Melody really doesn't know. Her past is all a blur. It captures Melody as it did Hitler. The Doctor arrives in evening clothes. He asks whom she killed. He uses a sonic cane to scan the Teselecta and learns Amy and Rory are inside it.

Melody tries to flee, but is recaptured. The Doctor demands they leave her alone and asks who they are. The Teselecta explains that as a form of justice, they visit unpunished criminals at the ends of their lives and "give them hell", agonising pain, while the timeline continues. The Doctor asks who wants him dead and Amy persuades the captain to tell him. It says the Silence are behind the plot to kill him. They are a religious cult who believe "silence will fall" when the oldest question in the universe is asked. It does not know what the question is. The Teselecta resumes torturing Melody.

The Doctor tells Amy to save her daughter. She uses the sonic screwdriver to turn off the crew's security clearances. The antibodies attack them and they teleport to safety. Amy uses a microphone to ask the Doctor for help. The antibodies are politely threatening Rory and her again. The Doctor struggles against his painful death. He crawls towards the TARDIS, shocking Melody that he still cares. The Doctor asks for her help, using her name, River. Melody demands to know who River is.

Inside the Teselecta, Amy and Rory are cornered by the antibodies. They accept their doom. Suddenly, the TARDIS materialises around them. They begin to thank the Doctor. Instead, they find a shaken Melody at the console, saying she flew the TARDIS. It taught her how.

They go to the Doctor, but he says there is no way for him to survive. He asks to speak to Melody. He asks her to find River Song, whispers something in her ear and dies. Melody asks who "River Song" is. Amy orders the Teselecta to show them. It shifts into the form of Melody's current incarnation. Melody learned that she is River Song. Amy and Rory ask Melody what the Doctor whispered in her ear. She does not answer this, but asks her parents if the Doctor is "worth it". They don't understand her question, but agree he is. Melody kisses the Doctor and gives up all her regenerations to save him.

Melody wakes in the greatest hospital in the universe. The Doctor leaves her a TARDIS blue diary. They must leave her to find her own way back to them.

In 5123, Melody, now calling herself River Song, applies to study at the Luna University. When asked why she wants a degree in archaeology, she says she is "looking for a good man".

Cast

 * The Doctor - Matt Smith
 * Amy Pond - Karen Gillan
 * Rory - Arthur Darvill
 * River Song - Alex Kingston
 * Mels - Nina Toussaint-White
 * Amelia Pond - Caitlin Blackwood
 * Young Mels - Maya Glace-Green
 * Young Rory - Ezekiel Wigglesworth
 * Zimmerman - Philip Rham
 * Carter - Richard Dillane
 * Anita - Amy Cudden
 * Jim - Davood Ghadami
 * Harriet - Ella Kenion
 * Adolf Hitler - Albert Welling
 * German officer - Mark Killeen
 * Professor Candy - Paul Bentley
 * Nurse - Eva Alexander
 * Female teacher - Tor Clark

Uncredited cast

 * Teselecta workers - Claudio Laurini, Dennis Gregory, Victoria Tomas, Jon Davey, Richard Knott, Kristian Arthur

The Doctor

 * The Doctor covertly switches a gun for a banana.
 * The Doctor adds to his rules:
 * Rule 1: The Doctor lies.
 * Rule 7: Never run when you are scared.
 * Rule 27: Never knowingly be serious.
 * Rule 408: Time is not the boss of you.

The Doctor's items

 * The Doctor gives Amy his sonic screwdriver.
 * The Doctor uses a sonic cane.
 * The Doctor gives River a brand new TARDIS-shaped diary to prepare her for the anachronistic meetings that are going to happen between them.

Companions of the Doctor

 * Rose Tyler, Martha Jones and Donna Noble all appear as holograms of the TARDIS voice interface.

Foods and beverages

 * The TARDIS' projection of Amelia mentions fish fingers and custard.

Locations

 * River is confronted by the Teselecta at the Hotel Adlon.

Religion

 * The Silence are not a species, but a religious organisation of sorts.

TARDIS

 * The temporal grace in the TARDIS, which supposedly prevents weapons fire, is said by the Doctor to be a "clever lie".
 * The TARDIS has extractor fans which work, much to the Doctor's surprise.

Culture

 * Before punching out the Nazi and taking his bike, Rory shouts 'Heil!'

Story notes
The first BBC America broadcast of the episode includes an extra scene which aired during a commercial break. It was sponsored by AT&T. As written by Steven Moffat, it is an extension of the motorcycle chase sequence with Rory and Amy. It is presented in animation/motion comic format. Lasting sixty seconds and produced by Double Barrel Motion Labs, the scene was originally promoted as intended for inclusion in the Series 6 DVD/Blu-ray releases, but as of early November 2011, this has not happened. The ad/motion comic was only seen in America.
 * A week and a day before this episode was broadcast in the US and two days before it was broadcast in the UK, the Torchwood episode Immortal Sins was broadcast. In it, a Brainspawn attempted to rewrite history by enabling the Third Reich to win the Second World War.
 * This is the first episode of the autumn half of the series. The spring half concluded on 4 June with A Good Man Goes to War. In addition, Amy says the Doctor has had all summer to find Melody, making the in-universe present day synchronised with real time.
 * This was Richard Senior's television directorial debut.
 * This is the second time that companions of the previous two Doctors have been mentioned or seen in a proper episode since The End of Time; Rose Tyler was previously seen (briefly) in The Lodger.
 * The images of all the former companions are taken from publicity shots. The projections of Rose and Donna are publicity images from Series 4. That of Martha is from a publicity image for Series 3.
 * The Doctor makes the "Doctor Who?" running joke.
 * The car Mels steals is a Chevrolet Corvette, third generation (68-82). It is the same model of car featured in the film and the mini-series From the Earth to the Moon.
 * The layout of the Teselecta's bridge is reminiscent of that of the Enterprise and other Federation starships from the television series Star Trek.
 * The TARDIS' voice interface tells the Doctor he will be dead in thirty-two minutes. Coincidentally in-universe, the invitation the future Doctor sent out to everyone in The Impossible Astronaut, to meet at Lake Silencio for the Doctor's death, was for 4:30pm and according to the biographical information the Doctor is shot during regeneration and killed at 5:02pm.
 * The hand gun that Mels pulls out is an IMI Jericho 941.
 * Harriet mentions the Teselecta having transformed into Rasputin. Tom Baker played Rasputin in the movie Nicholas and Alexandra.
 * In Mels' first scene in the episode, her face cannot be seen due to the sun's glare behind her. She moves her body to block the sun and her face is shown, much like the first scene of River in The Impossible Astronaut.
 * Melody Pond says, "Hello Benjamin", to the Doctor. The Doctor previously claimed Scotland Yard's code name for her was Mrs Robinson. (TV: The Impossible Astronaut) Both reference the movie The Graduate, in which a younger man, Benjamin, is seduced by an older woman, Mrs Robinson.
 * In the Leadworth Chronicle, a story with the headline "BACK OF THE NECK" can be seen. This is a reference to the weakness of the Sontarans. (TV: The Poison Sky)
 * This episode introduces a new article of clothing for the Eleventh Doctor that he continues to wear for most of the remainder of Series 6 - a green, double-breasted moleskin coat with six pockets and six gold buttons.
 * Arthur Candy was introduced in the short story Continuity Errors, roughly fifteen years earlier. As such, this marks the first televised appearance of a character introduced elsewhere.
 * Mels' regeneration marks the first time a regeneration has been shown on screen where the person has short sleeves instead of long sleeves, proving that the body gives off regeneration energy, and not just the hands and head.

Ratings

 * UK Overnight: 6.2 million
 * UK Final: 8.1 million

Myths

 * The Daily Mirror reported that Rose Tyler, Martha Jones and Donna Noble would appear in this episode. This was partially true. Images of all three appeared but these were avatars for a TARDIS interface, rather than the characters themselves. All images used were promotional images.
 * Some viewers speculated that when River resurrected the Doctor, he absorbed all of River Song's remaining regenerations. If this is true, as River only regenerated twice, the Doctor might now have twenty-two regenerations, instead of the standard twelve. This was proven incorrect by the Doctor himself in The Time of the Doctor, as he confirmed he had reached the natural end of his regeneration cycle and could not change for a thirteenth time.

Filming locations

 * Swansea, Wales.

Production errors

 * When the Doctor and the TARDIS make their first appearance, they point right, towards Amy and Rory's car. However, when the camera zooms out, the Doctor and TARDIS are looking down, and not towards Amy and Rory. This also causes an error when Mels drives through the word Doctor.
 * During the sequences of flashbacks explaining how River and the Doctor obtained and swapped guns right after the former's regeneration, River's uttering of the lines sound a bit more rushed, making it obvious that the original and flashback shots of the scene are two different takes.
 * When Rory asks, "How can they just disappear?" two antibodies appear, but in the next shot there are three.
 * When the poisoned Doctor is in the TARDIS he has one of his arms up on the bannister; in the next shot he has it by his side.
 * When the Teselecta's shock absorbers are malfunctioning, the captain's cup falls and can be heard smashing, but when the camera zooms out, there is no evidence of this.
 * Although Mels is shot by Adolf Hitler, resulting in her regeneration, when she stands up there is no sign of blood or a hole in her dress as the regeneration begins.

Continuity

 * The Doctor mentions "Vampires in Venice". (TV: The Vampires of Venice)
 * The Doctor speaks about River at Demon's Run. (TV: A Good Man Goes to War)
 * The Doctor has previously suffered poisoning serious enough to necessitate regeneration. (TV: The Caves of Androzani) However, on that occasion he still had regenerations to use, whereas here the Doctor has already exhausted all twelve of his regenerations (TV: The Time of the Doctor) due to varying circumstances. (TV: The Night of the Doctor, Journey's End )
 * When the Teselecta takes on the form of River Song, she is wearing the same dress she wore in America and at Demons Run. (TV: Day of the Moon, A Good Man Goes to War)
 * Rory punches two people in the jaw to knock them to the ground. Rory (as an Auton) previously did this to the Doctor when he deliberately provoked his anger to test if he really was the original Rory. (TV: The Big Bang)
 * Its revealed that River is the person who "killed" the Doctor at Lake Silencio and it is a fixed point in time. This also confirms that the man River is in prison for killing (TV: The Time of Angels, Flesh and Stone) is the Doctor.
 * River begins studying archaeology. (TV: Silence in the Library)
 * The TARDIS' projection of Amelia mentions fish fingers and custard. (TV: The Eleventh Hour)
 * Melody mentions regenerating into the toddler form of Mels in New York. (TV: Day of the Moon)
 * The Doctor switches Melody's gun for a banana, as he previously did to Jack Harkness. (TV: The Doctor Dances)
 * River reveals she learned how to pilot the TARDIS from the TARDIS herself. (TV: The Time of Angels)
 * A group of soldiers aim their guns at River, echoing how it happened likewise for the Doctor several times. (TV: Aliens of London, World War Three, Dalek, Army of Ghosts, Victory of the Daleks)
 * The Doctor tells Melody, "Rule one: the Doctor lies." (TV: The Big Bang) One of the first things the Doctor hears River say is "I'm always lying." (TV: Silence in the Library)
 * The Doctor leaves a diary by River's bedside as a gift. Here, it is seen to be brand new. By the time the Doctor first encounters it, years later from River's perspective, the diary has been used and roughed up so much that it is on the verge of falling apart. (TV: Silence in the Library)
 * The Teselecta data console states the Doctor's TARDIS is a Type 40 Mk 3 TT Capsule, very similar to its official Time Lord designation. (TV: The Deadly Assassin)
 * The Teselecta crew mentions something in "Kennedy"'s timeline is not a fixed point in time. While this is probably a reference to the assassination of American President John F. Kennedy (an event witnessed by the Ninth Doctor (TV: Rose, and see also PROSE: Who Killed Kennedy)), it could refer to the death of his brother, Senator Robert F. Kennedy, or another event involving a member of the Kennedy family.
 * The Megara, who appeared in The Stones of Blood, functioned as "justice machines".
 * It is mentioned twice that River uses her "remaining" regenerations to revive the Doctor, implying that she has a fixed amount. The ability to transfer regeneration energy from one regeneration-capable individual to another has been suggested before. (TV: Mawdryn Undead, Doctor Who (1996), The Ultimate Foe)
 * River has previously used a type of lipstick to her advantage. (TV: The Time of Angels, The Big Bang) This time, she uses a version made from the poison of a Judas tree. Captain John Hart previously used a similar poisonous lip gloss that caused paralysis, and if left untreated for longer than two hours, death. John claimed that he may have even learned about the poison lip gloss from Jack Harkness. (TV: Kiss Kiss, Bang Bang) River's parting words to The Doctor before jumping out the window were also, "Kiss, kiss!"
 * River recovers completely after being shot several times by German soldiers; she is still within the first fifteen hours of her regeneration. The Tenth Doctor recovered from a severed hand while fighting a Sycorax under similar circumstances. (TV: The Christmas Invasion) Romana tried several forms after her first regeneration. (TV: Destiny of the Daleks)
 * When first detecting there are life forms inside the Teselecta, the Doctor wonders if it is bigger on the inside.
 * The TARDIS has materialised before inside a smaller object containing miniaturised life forms in a compression field. (TV: Carnival of Monsters)
 * Mels says, "See you later, Time Boy" during a flashback. Donna Noble called the Doctor, "Time Boy". (TV: Journey's End)
 * The Doctor says, "Spoilers", when Melody asked who River was, a word frequently used by River herself later in her timeline. (TV: Silence in the Library, et al.)
 * The Doctor previously said that "Time is not the boss of me." (TV: The Time of Angels)
 * Amy had a picture of herself and (apparently) Mels on a table in her bedroom. (TV: Flesh and Stone)
 * Teselecta Amy tells the Doctor that the Silence is not a species. The Slitheen said a similar thing to the Doctor. (TV: World War Three)
 * The Fourth Doctor has previously asserted that someone he was leaving behind will be more than "fine." (TV: Warriors' Gate)
 * The Eleventh Doctor changes his clothing in the midst of a long and painful death. The Tenth Doctor apparently did the same thing just before regenerating, changing into an undamaged version of his brown suit, along with a new tie, before dropping off Wilfred Mott. (TV: The End of Time)
 * While lecturing Mels, Amy asks her, "Who steals a bus?!" Sarah Jane Smith and Lady Christina de Souza do. (TV: Invasion of the Bane, Planet of the Dead)
 * The Doctor tells Rory to put Hitler in the cupboard. A similar exchange was once shared between Claire and George: "What do we do with things we don't like?" "We put them in the cupboard." (TV: Night Terrors)
 * When asked by the Doctor about why he never met her at Amy's wedding, Mels replies "I don't do weddings". She attends the wedding as River Song (who apparently does do weddings) and leaves her blank diary for Amy. (TV: The Big Bang)
 * The Ninth Doctor had previously been shown to anticipate and effectively neutralise assassination attempts against him by Blon Fel-Fotch Passameer-Day Slitheen. (TV: Boom Town)
 * Amy states that the sonic screwdriver can be used by "pointing and thinking". The Tenth Doctor previously indicated that the Vashta Nerada could use Proper Dave's Neural relay by simply pointing and thinking. (TV: Forest of the Dead)
 * Melody materialises the TARDIS around her parents, causing them to appear in the console room. This has been done before to various people and objects:
 * The Fourth Doctor materialised his TARDIS around The Master's TARDIS while it was disguised as a police box. (TV: Logopolis)
 * The Fifth Doctor proposed doing such again to The Master's TARDIS while it was disguised as a Concorde. (TV: Time-Flight)
 * The Ninth Doctor materialised around Rose Tyler and a Dalek. (TV: The Parting of the Ways)
 * The Tenth Doctor may have done the same in order to save the crew of Bowie Base One before it exploded. (TV: The Waters of Mars)
 * The Doctor would again materialise the TARDIS around Amy and Rory (along with Rory's father, Brian). (TV: Dinosaurs on a Spaceship)


 * Because the Doctor did not answer his phone, Amy and Rory get the Doctor's attention by creating a crop circle in Leadworth that spells out his name. (WC: Prequel (Let's Kill Hitler)) River Song took similar measures to contact the Doctor by defacing a cliffside on Planet One with writing that translated into, "HELLO SWEETIE ΘΣ Φ ΓΥΔϟ" (ΘΣ Theta Sigma) for not answering her calls. (TV: The Pandorica Opens)
 * The Doctor feels guilt regarding his previous companions Rose Tyler, Martha Jones, and Donna Noble.
 * The Fourth Doctor told Eldrad that the TARDIS interior was "in a state of temporal grace", so weapons would not work inside of it. (TV: The Hand of Fear) When asked about this seeming to not always be the case, the Fifth Doctor simply said that "nobody's perfect". (TV: Arc of Infinity)
 * The Doctor tells the TARDIS's hologram of Amelia to, "Come along, Pond." (TV: Victory of the Daleks, The Big Bang, Death of the Doctor, A Christmas Carol)

Home video releases
This episode, along with the rest of the second half of series 6, was released on DVD and Blu Ray on the 10 October 2011.

The complete series 6, which included the first and second half of the series, was released on DVD and Blu Ray on the 21 November 2011.