Turn Left (TV story)

Turn Left was the eleventh episode of the fourth series of Doctor Who. It was the first Doctor-lite episode to focus on the main companion without the Doctor and marks the first main reappearance of Rose Tyler. It also showed that most of the companions that the Ninth Doctor and Tenth Doctor acquired would have died undoing the events that occurred after the Empress of the Racnoss' attack on London. Much of series 3 and 4's events set on present day Earth would still occur, but would have cost more lives without the Doctor's intervention. The Master would not have been present in his Harold Saxon persona as the Doctor would not have been alive to go to the year 100 trillion to allow him to escape the end of the universe.

Synopsis
On the planet Shan Shen, Donna meets a fortune teller, who launches Donna into a world based on one question: "What would happen if Donna never met the Doctor?" Without the Doctor, the whole world is in ruin and a mysterious blonde woman tries to warn Donna of the oncoming darkness...

Plot
The Doctor and Donna are on the planet Shan Shen, mixing with the locals. Donna wanders away from the Doctor to explore as he's too busy chatting away with a merchant. A mysterious fortune teller asks if she wants her future told, but Donna refuses. The fortune teller then says the reading is free for those with red hair. As the fortune teller looks into Donna's past, she sees there is a man in her life that changed everything. Donna wonders why she is looking into the past and experiences a flashback, but the fortune teller dismisses it. The teller asks Donna what event lead to her meeting with the Doctor and Donna says it was in June 2007. At that time, Donna and her mother were in a car at a T-junction, arguing about her future. Sylvia tried to persuade Donna to turn right and ask businessman Jival Chowdry for a job; but Donna turned left to go to her planned temp job at H.C. Clements. After experiencing another flashback, Donna is now panicking, but the fortune teller asks her what would have happened if she never met the Doctor as something crawls onto Donna's back. Scared, Donna falls under the fortune teller's influence and, in the past, she gives in to her mother's nagging and turns right, altering the course of her life as well as the future of all existence.

It is Christmas Eve 2007, and Donna is at a Christmas Party with the rest of the staff from her workplace. She has just been promoted to Jival Chowdry's personal assistant. Suddenly the Racnoss Webstar attacks London, and is destroyed by the army at a terrible cost. During the chaos, Alice stares at Donna's back, looking terrified. When Donna acts astonished that Alice's attention is focused on her despite the ongoing chaos, Alice, terrified, says that there is something on Donna's back. After this, Donna runs to the Webstar's general location. There she finds an ambulance. Near the ambulance and a group of UNIT vehicles, Donna overhears a UNIT officer telling someone that they found a body. Harris says that the now dead person was able to stop the "creature", but in the end, he says that "The Doctor is dead." As the body is loaded into an ambulance, a sonic screwdriver falls out of the body's hand. As Donna walks away, Rose Tyler comes running down the street and asks for information about the body that has just been loaded into the ambulance. Rose is stunned to hear that it was the Doctor, despite Donna's assurances that it could have been any doctor. In April 2008, Donna is fired from her job. Chowdry tries to tell her that he has to lay people off because half of his contracts are on the other side of the river. Even though it has been several months since the Racnoss attack, the Thames is still closed off. Meanwhile, the Royal Hope Hospital is mysteriously transported to the Moon. When it returns, there is only one survivor: medical student Oliver Morgenstern, who relates the terrible events. As in the original timeline, the hospital had been moved by the Judoon and infiltrated by a Plasmavore. Sarah Jane Smith (at the hospital with her son Luke Smith and his friends Maria Jackson and Clyde Langer) filled the Doctor's role, and stopped the MRI from irradiating the Earth - but, without the Doctor, the humans couldn't find a way back to Earth, and all suffocated. Oliver Morgenstern tells reporters he only survived when fellow medical student Martha Jones gave him the last of her oxygen.

As Donna digests the terrible news, Rose reappears, stumbling out of an alleyway, and after a little discussion, she suggests to Donna that she go to the country for Christmas 2008.

Donna takes Rose's advice, and treats her mum and grandfather to a Christmas holiday in the English countryside. On Christmas morning 2008, they watch the telly in disbelief as a replica of the Titanic falls on Buckingham Palace. The three run outside and watch, horrified, as a mushroom cloud rises above London.

Now refugees since all of southern England has been flooded with radiation, the Nobles are forced to move to Leeds. France has closed its borders. They are allocated a house that is shared with two other families.

In 2009, the United States pledges to help Britain with monetary relief but must abandon the plan when their own crisis strikes: sixty million Americans are turned into Adipose. Since London no longer exists, Adipose Industries had targeted the USA.

Some time later, Donna finds soldiers firing at cars when the Sontarans activate the ATMOS devices, covering the Earth with a poisonous fog. A soldier notices something on Donna's back and holds her at gunpoint, but she is released when nothing is there. That night, Donna meets Rose for a third time. Rose explains that the Torchwood team, aboard the Sontaran ship, are trying to stop the catastrophe. Suddenly, the sky is cleared by an atmospheric converter. Gwen Cooper and Ianto Jones have given their lives to achieve this, and Captain Jack Harkness has been stranded on the Sontaran homeworld.

Rose refuses to tell Donna her name. She only says that she has "crossed reality" (coming from the parallel world on which she was trapped in Doomsday), and tries to explain that Donna had saved the Doctor's life in an alternate timeline, though Donna insists that she had never met him. Rose warns Donna the coming "darkness" threatens every single universe. Donna tries to walk away, but Rose tells her that she will have to go with her when she is ready and that she has three weeks to decide. Rose warns Donna that when she comes with her, Donna will die. Then she disappears.

Three weeks later, the genial Italian family in Donna's house is evicted as England is now "only for the English". Since the oceans are closed off, they must be taken to a "labour camp". Wilfred says, "That's what they called them the last time," alluding to the concentration camps of World War II. Later at night, Donna and Wilf talk about recent events while looking through his telescope. He notices that the constellation of Orion has gone, though there are no clouds. As the stars disappear from the sky, Donna finds the younger woman, and tells her that she is ready.

Rose takes Donna to a UNIT base and shows her the TARDIS - salvaged from beneath the River Thames - which is dying after the Doctor's death. Using technology scavenged from the TARDIS, Rose switches on a light which reveals what is on Donna's back: a 'Time Beetle'. Donna is horrified and begs Rose to get it off of her. However, Rose explains that it "feeds off time by changing time" and that she thinks the beetle is in a state of flux, although when Donna asks what that means, Rose says she doesn't know, but that it's something the Doctor would say. She also says the beetle cannot be removed; When Donna becomes angry that Rose said she was special but Donna thinks it wasn't her, but the beetle, Rose says that actually they're getting separate readings from Donna that make it seem like reality is bending around her.

In order to set things right, they prepare to send Donna back in time to stop her past self from turning right. Donna agrees and is elated by the belief that rather than dying, "This whole world will blink out of existence but a better world takes its place - the Doctor's world." Rose remains silent. Donna tries to get confirmation of her belief, but Rose only replies sadly "I'm sorry". Before Donna can learn what will happen, she is sent back in time.

Donna lands in June 2007, elated that the time travel worked, but quickly realises that she is a half a mile away from her past self and has only got four minutes to prevent her past self from turning right. She tries to run to herself, but realises that she will not make it in time. Donna realises what Rose meant about her death, and she sees a haulage truck coming along that has just passed by her past self. She steps in front of the truck, which screeches to a stop.

Before Donna dies, Rose appears and whispers something into her ear to tell the Doctor. At the intersection, Donna's past self decides that instead of sitting in backed up traffic, she will turn left.

As the original timeline reasserts itself, Donna regains consciousness in the fortune teller's stall on Shan Shen. The baffled and terrified fortune teller flees, screaming, "You were so strong. What are you!? What will you be?!" The Doctor, who has been blissfully unaware of all that's happened, enters and an emotionally spent Donna collapses into his arms. When he asks why, she simply replies, "I don't know!" and proceeds to hug him again.

Upon examining the beetle, the Doctor tells Donna that it is part of the Trickster's Brigade and that normally it affects one person and the universe compensates (as happened to Sarah Jane Smith), but in Donna's case, it created a parallel universe. The Doctor muses on all of the coincidences surrounding Donna: the fact that she had two parallel worlds that formed around her (this one and the one in the CAL computer) and that he's met her and her grandfather twice. "In the whole wide universe, I met you again," he notes. The Doctor concludes that they seem to be somehow linked. Donna tells the Doctor she is nothing special, but he counters saying that she's "brilliant". Hearing that triggers Donna's memories of the parallel world and she mentions the blonde woman to the Doctor. When asked if she remembered the blonde woman's name, Donna said she was never told it, but she does remember the two words the blonde woman whispered into her ear: "Bad Wolf". Terrified, the Doctor runs out into the market square to see the words 'Bad Wolf' everywhere: on posters pasted onto the walls, on the ceremonial flags hanging over the market, even on the TARDIS itself. Inside the TARDIS, the control room is glowing red and the Cloister Bell is ringing. When Donna asks what's going on, the Doctor replies, looking horrorstricken, "It's the end of the universe."

Cast

 * The Doctor - David Tennant
 * Donna Noble - Catherine Tate
 * Rose Tyler - Billie Piper
 * Wilfred Mott - Bernard Cribbins
 * Sylvia Noble - Jacqueline King
 * Rocco Colasanto - Joseph Long
 * Capt. Magambo - Noma Dumezweni
 * Fortune Teller - Chipo Chung
 * Mooky Kahari - Marcia Lecky
 * Veena Brady - Suzann McLean
 * Alice Coltrane - Natalie Walter
 * Man in Pub - Neil Clench
 * UNIT Soldier - Clive Standen
 * Jival Chowdry - Bhasker Patel
 * Female Reporter - Catherine York
 * Morgenstern - Ben Righton
 * Spanish Maid - Loraine Velez
 * Studio News Reader - Jason Mohammad
 * Housing Officer - Sanchia McCormack
 * Soldier #1 - Lawrence Stevenson
 * Trinity Wells - Lachele Carl
 * Woman in Doorway - Terri-Ann Brumby
 * Soldier #2 - Paul Richard Biggin

Individuals

 * Jack Harkness
 * Gwen Cooper
 * Ianto Jones
 * Sarah Jane Smith
 * Maria Jackson
 * Clyde Langer
 * Benito Mussolini (When Donna is yelling at the father during the "sea shanty" scene: "Listen Mussolini!"--noting his Italian descent. Benito Mussolini was the Fascist Dictator of Italy during WWII)

Events in the alternate timeline

 * The Doctor dies and does not regenerate for some reason whilst defeating the Empress of the Racnoss under the Thames. In the episode The End of Time, the Doctor states that if he dies before he has a chance to regenerate, he will die for real, which might explain why he died in the alternate timeline. He can regenerate from things like radiation or gunshot wounds because they don't kill him immediately.
 * Private Harris, one of the privates who was programmed by the Sontarans in The Sontaran Stratagem, is at the scene when the Doctor's body is loaded into the ambulance after the Racnoss attack. He reports to his commander about the incident.
 * Martha Jones, Sarah Jane Smith, Maria Jackson, Luke Smith and Clyde Langer all die in Royal Hope Hospital after it is transported by the Judoon to the Moon, though Sarah Jane succeeds in stopping Florence Finnegan's MRI weapon.
 * The starship Titanic crashes into Buckingham Palace, killing everyone in the greater London area and contaminating southern England - bar Devon & Cornwall - with radiation.
 * The destruction of London triggers a societal collapse in Great Britain, which becomes a police state that closes its borders, and leads to the introduction of concepts such as forced labour camps.
 * The March of the Adipose occurs in America instead of the UK; without the Doctor to stop it, Sixty million people are killed (vs 10 thousand in the original timeline), preventing the US from aiding Great Britain, and accelerating the UK's decline.
 * Gwen Cooper and Ianto Jones die whilst assaulting the Sontaran warship. Captain Jack Harkness, who is unable to die due to his immortality, is instead transported to the Sontaran homeworld.
 * There is no one to prevent the ATMOS devices from decimating the population of the Earth until Torchwood manages to set the gas on fire, although the UK is spared this as, due to the destruction of London, not to mention the lack of petrol, ATMOS never came into widespread use there.
 * Non-UK citizens are placed in camps, as the borders have been closed to other countries, possibly meaning the country is now under a Fascist regime.
 * Rose Tyler appears to be working with UNIT.
 * On the television news it's mentioned that Sarah Jane Smith used to work for Metropolitan.
 * It is likely that, because of the Doctor's death, the Master is stuck at the End of the Universe because the TARDIS never went there, explaining the absence of Harold Saxon during these events.
 * Despite the Doctor and Donna never having gone back in time to stop the Pyrovile from taking over Pompeii (and subsequently, the world), the Pyroviles' plans were somehow stopped in the alternate timeline, as evident by the Earth not being a new Pyrovillia.
 * Similarly, the Carrionite invasion was also somehow disrupted without the help of the Doctor and Martha Jones.
 * It is likely that the events after the Doctor's death resulted in preventing Richard Lazarus' experiment resulting in many deaths of his mutation affected from the Genetic Manipulation Device.
 * The plans of the Cult of Skaro in 1930s Manhattan also failed despite the Doctor not stopping them.
 * Lastly, the stars can be seen going out in the night sky as Donna and Wilfred stargaze, indicating that the reality bomb has been detonated. Its effects are sweeping through the cosmos and other universes, disassembling them out of existence, and the complete destruction of all reality is imminent.

Story notes

 * This is the first story to feature Rose in a starring role since TV: Doomsday.
 * Despite being billed in the opening credits and featuring prominently in the episode, Rose is never referred to by name.
 * Billie Piper was seen at the end of Partners in Crime, and had short cameos in The Poison Sky and Midnight. The Partners in Crime cameo was filmed during production of Turn Left, as was the short piece of footage used in Midnight and The Poison Sky. This means no less than three directors would have been at work on the Doctor Who set during the production schedule of Turn Left - the main episode's director, Graeme Harper, the director of Partners in Crime, James Strong, and the director of Midnight, Alice Troughton.
 * Unusually, the episodes featuring Piper were filmed relatively early in the production of the season, which allowed a clip of Rose from this episode to be included in the cinema trailer released in advance of the season being broadcast.
 * Chipo Chung last appeared in TV: Utopia as the Malmooth, Chantho, Professor Yana's personal assistant. She plays the fortune teller in this story.
 * This is the 'Doctor-lite' episode of the series, similar to Love & Monsters and Blink, albeit with a much darker storyline. Unlike previous Doctor-lite stories, however, the focus is given to the companion, rather than her also taking a minor role. They used the same scheduling trick in the previous episode, Midnight, which featured virtually none of Donna. These episodes allow the production team to complete fourteen episodes (including the Christmas episode) in a schedule originally designed to complete thirteen. A second team can be filming the "extra" episode, with the main cast filming only a day or so. Their footage is judiciously spread through the episode to give the impression of a larger interaction, although in the case of Turn Left, David Tennant's participation was restricted to the opening scene and epilogue, with a body double used for the scene where Rose and Donna witness the Doctor's dead body being loaded into the ambulance.
 * A reference to something on Donna's back was last heard in The Fires of Pompeii when Lucius Petrus Dextrus saw into the future.
 * In Doctor Who Magazine it said that Donna will receive a free tarot card reading and find out something bad is going to happen. When she is receiving it there will also be something behind her lurking in the curtains. The Tarot person will also look for a specific event in Donna's past. The episode, as broadcast, takes place on a Chinese-influenced alien world with no reference to Tarot.
 * "The bees are disappearing" is quoted again in this episode, this time by Donna's mother, Sylvia Noble. This is a real-world phenomenon, called Colony Collapse Disorder, the incidence of which increased sharply in late 2006, and the cause of which has not been identified. In "The Stolen Earth" and "Journey's End," the cause of the disappearance is revealed.
 * A recurring theme in previous episodes hinted that Donna would die in the future which occurs in this episode. However, this was an alternate reality Donna who sacrificed herself in order to prevent her past self from taking the wrong turn thus forcing her to meet the Doctor as was planned.
 * Part of this episode is filmed in China Town, though not the one in London, but recreated in Cardiff. Chinese people living in South Wales were invited to be background extras via Facebook at the end of 2007. They had to reply to the Doctor Who casting crew with their name and sizes for costumes to be made for them and they were paid approx £70 for the day. David Tennant was seen in 'China Town' when he took time out of filming though staying on location to appear on Blue Peter to appeal to viewers to donate shoes to their Shoebiz appeal.
 * Donna is told she can have her fortune told for free because she has red hair. This is a reference to Chinese culture, since red is considered very lucky in China. It's also a common carny trick to draw people into the attraction; half off for lovely ladies, men wearing hats, anything that matches some characteristic of the person being appealed to.
 * Graeme Harper's penchant for including a distorted image of a main character is present in this story. Though not included in every single episode he's directed for BBC Wales, it's seen often enough in the majority of his stories to be considered something of a directorial "signature". More typically achieved through the use of refraction (The Unicorn and the Wasp, Army of Ghosts, Journey's End and Utopia), here the motif is continued through the use of reflection. The theme of Donna's multiple worlds is caught through the simple use of mirrors, much as the notion of investigation was conveyed by the use of magnifying glasses in earlier stories.
 * According to Russell T Davies on Doctor Who Confidential, this episode is the "cheap episode", as he wanted the TARDIS to be on fire, but the budget didn't allow for the effect.
 * A variation of 'The Wall Theme', (The Wall Theme is a variation of Rose's Theme, played in Doomsday.) with added guitar parts, is played before Donna is sent back in time.
 * Two pieces of background pop music return from other episodes. In the scene in which Donna goes out with her friends to celebrate her new job as Chowdry's personal assistant, the song "Merry Xmas Everybody" by the glam rock band Slade can be heard (first heard on Mickey's radio in The Christmas Invasion). This was also playing during Donna's wedding reception in The Runaway Bride.
 * Billie Piper states in the accompanying Doctor Who Confidential episode that she had forgotten how to play Rose, and needed to watch past episodes to remind herself.
 * This isn't the first time a Doctor Who story has examined a "What if..." scenario involving the Doctor's influence on a person's life. A similar storyline involved Eighth Doctor companion Samantha Jones, depicted in two wildly diverging timelines (PROSE: Unnatural History).
 * The revelation that the events leading to the creation of the alternate timeline originated from the Trickster is a direct reference to a character from The Sarah Jane Adventures and, indirectly, the events of TV: Whatever Happened to Sarah Jane? in which Sarah Jane Smith was similarly taken out of time. This marks the first direct crossover between the spin-off and Doctor Who (discounting Sarah Jane's connection to the parent series, of course). The main cast of the spin off are also stated to have died during the events.
 * At one point the Nobles and the Italian family take part in a singalong to Queen's "Bohemian Rhapsody". This tune has been the basis for two practical jokes featured on Who franchise-related blooper reels: a group of Sycorax are shown singing it in the Series 2 blooper reel, while the Series 2 gag reel for Torchwood shows the cast cutting up to the same song.
 * As is routine for post-2005 Doctor Who, a "NEXT TIME" trailer for the next episode is shown at the end of the episode.

Ratings

 * Official Broadcasters' Audience Research Board (BARB) - 8.09 million viewers. Turn Left was the 4th most watched across all channels on British television for the week.

Myths and rumours

 * Many fan reviews and discussions of this episode have noted that, for reasons unknown, Rose speaks with a noticeable lisp in many of her scenes - a lisp not present when she was last on the show; a frequently cited example being when Rose tells Donna she's the most important woman in all of creation. Among the speculated reasons as to why is Billie Piper's statement on Doctor Who Confidential (see above) that she had forgotten how to play Rose -- a character who speaks with a more working-class accent than Piper's natural voice. Rose is starting to speak more like the Doctor himself as she has become more like him in the sense of using technobabble and not wishing to accept salutes, nor does she reveal her name. The lisp is present, but less noticeable in the next two episodes and appears to be less noticeable (if not missing completely) in interior studio scenes as opposed to on-location filming. Also, the lisp is not present at all in Piper's Doctor Who Confidential interviews shot during production of the final three episodes, nor is it heard during the instalment of David Tennant's Video Diaries pertaining to the production of The Stolen Earth/Journey's End in the Series 4 DVD box set.
 * The opening credits are reversed, showing the TARDIS moving in the opposite direction in the time vortex. As broadcast and released to DVD, the opening credits are presented normally. The feature of the TARDIS being reversed could also be a teaser as the episode skews off into another world, and Donna turns right instead of left.
 * It was rumoured that the episode was going to be named The Doctor's Death.

Filming locations
to be added

Production errors

 * The sound and shaking of the Royal Hope disappearing is heard before it actually vanished, whereas in Smith and Jones the sound was heard during the incident.
 * When the Adipose are seen on the television the images are exactly the same as those seen in Partners in Crime, even though it is supposed to be happening in America.
 * If one looks closely when Rose shows Donna the TARDIS at the UNIT base, the interior of a police box can be seen through the open door instead of the TARDIS interior.
 * When Donna is making the decision to turn right or left, it is clearly raining on the car. However in any external shots, most notably when Donna has travelled back in time, it is not raining.
 * When Donna walks into the car in the first flashback, she enters the back door in the external shot, but, in the internal shot, is clearly entering the front door.
 * The scene of the Titanic spaceship crashing into Buckingham Palace is reused directly from TV: Voyage of the Damned, but the section of footage where the ship would barely miss the palace is omitted and replaced with a blinding light overlay to create the idea the ship has exploded, instead of animating a whole new sequence that graphically depicts its destruction (which would be costly on the series budget), showing the obvious cut-and-paste nature of the scene.

Continuity

 * This is the second time Rose was present at the death of someone she knew, who also ultimately died to correct the timeline. In TV: Father's Day, Rose was present at her father's death, which she prevented when she had come back in time with the Ninth Doctor. The resulting fracture of creating a parallel world caused chaos until that parallel Pete Tyler sacrificed his life to restore the original timeline. In this episode Rose is present at parallel Donna's death, which caused the original Donna to turn left instead of right, restoring the timeline. By coincidence, both parallel versions of Pete and Donna are hit by a car, and both die with Rose by their side.
 * Among other uses of the phrase "Turn Left" in the series: in TV: The Sontaran Stratagem the ATMOS kept saying, "Turn left"; Captain Jack mentioned telling someone they should have turned left during a joke in Boom Town; events leading to an alternate future were due to people 'turning right' instead of 'turning left' in PROSE: The Twilight Streets.
 * Like the TARDIS, Donna's car is blue. She often is seen wearing blue, and when leaving her job, she decides to keep a blue hole-punch, notable since for most of the series, the Doctor has been inadvertently punching holes in the fabric of the universe.
 * Bad Wolf returns as a warning for the end of the universe. Bad Wolf was last heard in TV: Doomsday.
 * "The Bees are disappearing" is said again in this episode, this time by Sylvia Noble.
 * The Cloister Bell is heard, again as a warning. It was last heard in TV: Time Crash.
 * Two phrases said by Lucius Petrus Dextrus in TV: The Fires of Pompeii come to fruition in this episode: "There's something on your back" and "She is returning".
 * The characters from The Sarah Jane Adventures are named in the news report as dead in the parallel timeline.
 * A UNIT soldier refers to regeneration. UNIT has extensive knowledge of regeneration, having directly been involved with the aftermaths of the regenerations of the Second and Third Doctors. The Brigadier himself is known to have met most of the Doctor's incarnations (both on screen and in the spinoffs), and UNIT was also involved with the newly regenerated Tenth Doctor in The Christmas Invasion.
 * In TV: The Sontaran Stratagem, Colonel Mace and Captain Price saluted the Doctor but he said, "Don't salute, please". When Captain Magambo saluted Rose, she told her not to salute as well. The difference is that this time Donna doesn't ask for a salute like she did in The Sontaran Stratagem.
 * The time beetle almost exactly parodies the Eight Legs from Planet of the Spiders. They are both arthropods, sit on the backs of humans, and can remain unseen.
 * Mirrors have been used for time travel in TV: The Evil of the Daleks and AUDIO: The Time of the Daleks.
 * A circle of mirrors was also used to expose and reveal the Mara (as is used here to reveal the beetle) in TV: Kinda, and a mirror was essential to the storyline of PROSE: Martha in the Mirror and, in a sense, of TV: Timelash.
 * There have been a few other instances of the Doctor 'dying' and events taking different courses. (PROSE: Blood Heat, COMIC: Final Genesis) The Doctor's apparent death during his eleventh incarnation is actually a fixed point in time, and an alternate timeline was created when attempts were made to prevent it. (TV: The Impossible Astronaut, The Wedding of River Song)
 * In TV: Army of Ghosts, Torchwood One operative Adeola Oshodi, who had been captured and reprogrammed by the Cybus Cybermen, lures her colleague to his death by telling him to "go to the left", where a Cyberman advance patrol lurks in the shadows.
 * When Donna, Wilf and Sylvia are watching the news report, the picture is said to be coming from the Guinevere range of satellites, which is the same range as the Guinevere space project first seen in TV:The Christmas Invasion.
 * Discounting minor modifications over the years, the replacement of the wording on the TARDIS exterior with "Bad Wolf" - and this appears to be a physical change given that the words are visible from the inside, too - marks the first time the TARDIS has undergone a physical change since Attack of the Cybermen. Although not indicated in dialogue, the fact the TARDIS is now adorned with the words "Bad Wolf" - but the words are gone by the time the vessel returns to earth in the next episode - suggests the chameleon circuit came into play. This could also be the result of the TARDIS' translation ability. Having previously shown the ability to make words appear in a certain language, it could make the words on the TARDIS appear in any form it wants. Finally, the change could have been caused by Rose while she was the "Bad Wolf" as part of her spreading the words through time. (TV: Bad Wolf, The Parting of the Ways)
 * Rose says to Donna, "I'm sorry, I'm so sorry," a phrase often uttered by the Tenth Doctor.
 * The improbability of the Doctor meeting anyone twice by accident is remarked on. Previous examples of such coincidence are the reunion of the Fifth Doctor and Tegan Jovanka in Arc of Infinity after Tegan's departure in Time-Flight, and meeting Sarah Jane Smith in TV: School Reunion. In the cases of Donna and Sarah Jane the reunion is less improbable than with Tegan, because they were both undertaking Doctor-like activities themselves. This subject is brought up again in The End of Time during the discussion between the Doctor and Wilf about the Doctor's impending regeneration.
 * The scenes set on Shan Shen take place in the 85th century according to REF: The Time Traveller's Almanac, although the book does not explain how this date was arrived at.
 * The Trickster previously told Sarah Jane Smith of his intention to use her to locate the Doctor so he could remove him from time. (TV: Whatever Happened to Sarah Jane?)
 * Advertisements for Henrik's are plastered on the double-decker buses passing through London during the assualt of the Webstar. One bus advertising Henrik's can be seen as a British military tank rolls into up and the soldier inside orders troops to fire on the Webstar. (TV: Rose, The Runaway Bride)

Home video releases

 * This story was released in the Series 4 DVD box set in November 2008 along with the rest of the series.
 * It was released as Series 4 Volume 4 with The Stolen Earth and Journey's End.