Journey's End (TV story)

"For this is my ultimate victory, Doctor! The destruction of reality itself!!"

- Davros

This is the 13th and final episode of Series 4 and featured 6 companions of the Doctor. It is a continued on a cliffhanger from Episode 12. As of July 2008 it holds the distinction of being the highest-rated episode in the history of the Doctor Who franchise.

Synopsis
The entire universe is in danger as the Daleks  activate their master plan to destroy reality itself. The Doctor is helpless, and even the  TARDIS  faces destruction. The only hope lies with the Doctor's secret army of companions– but as they join forces to battle Davros himself, the prophecy declares that  one of them will die.

Plot
The Doctor is regenerating inside the TARDIS while Donna Noble, Captain Jack Harkness and Rose Tyler watch in horror. However, the Doctor transfers his regenerative energy into the container which carries his severed hand. He has healed himself, but chosen not to change his appearance. The TARDIS is transported by the Daleks to the Crucible and rendered powerless. The Doctor, Jack, and Rose leave it, but Donna is distracted because she is hearing the sound of a heartbeat and while looking back, the TARDIS door slams closed. Before the Doctor can free her, the Daleks dump the TARDIS into a waste chute where it will be destroyed in the centre-core of the Crucible. As the TARDIS interior explodes around her, Donna collapses near the severed hand, she hears the heartbeat again and while touching the container energy flows between it and her. The hand bursts out of the container, and forms as a new Doctor, although this Doctor has only one heart and has picked up some of Donna's mannerisms. With his help, the TARDIS escapes destruction and gives the new Doctor and Donna time to come up with a plan.

In Torchwood Three, Gwen Cooper and Ianto Jones find themselves safely in a time lock created by Toshiko Sato, preventing the Dalek from entering but also preventing them leaving. Sarah Jane Smith is saved from two Daleks by Mickey Smith and Jackie Tyler, but in order to follow the Doctor, they lay down their guns and allow themselves to be captured, taken to the Crucible. Martha Jones says her goodbyes to her mother and makes for an abandoned castle in Germany where one of five Osterhagen stations is hidden, and waits for contact from the other bases.

Aboard the Crucible, Jack creates a distraction by shooting the Supreme Dalek with his revolver, but is exterminated by the Daleks; as the Doctor and Rose are taken to the Vault where Davros is held, Jack's immortality allows him to escape. With the Doctor and Rose contained, Davros explains that the 27 planets form an energy pattern that is then amplified into a "reality bomb", able to break apart the forces holding everything together. Mickey, Jackie, and Sarah Jane escape a test chamber where this effect is shown to the Doctor just in time. Jack finds his way to the three, and with a locket from Sarah Jane, creates a device that will implode the Crucible. Meanwhile, Martha makes contact with two other bases in China and Liberia. The Chinese counterpart wants to get it over and done with, but Martha, knowing the Doctor, first broadcasts a signal to the Crucible to give them (probably both Earth and the Daleks) a second chance, promising to use the Osterhagen key to detonate 25 nuclear warheads under the Earth's crust to destroy it and disable the reality bomb. However, the Daleks manage to lock onto their positions and beam Martha, Jack, Mickey, Jackie, and Sarah Jane, with the Transmat to the Vault where the Doctor and Rose are also being held captive. The Daleks prepare to activate the reality bomb that will wipe out all matter in this and every parallel universe through the rifts in the Medusa Cascade, but the new Doctor and Donna arrive in the TARDIS. Both, however, are stunned by shots from Davros. The reality bomb countdown reaches zero, but nothing happens; Donna has manipulated the controls to disable it. The Doctor recognises that the creation of the new Doctor has had an unintended side effect: Donna is now half Time Lord herself, sharing the Doctor's intellect. Donna and the new Doctor free the others, and with the help of the original Doctor, disable the Daleks and start to send the planets back to their proper time and space. Before Earth can be sent, the machinery is destroyed by the Supreme Dalek, who is then destroyed by Captain Jack. The original Doctor races into the TARDIS to replace the functionality of the broken machine. Realising that Dalek Caan has seen the end of the Dalek race and has been manipulating time to achieve this, the new Doctor (probably not kept back by guilt due to the influence of Donna's personality) uses the remaining machinery to destroy all of the Daleks and their fleet. The rest of the companions flee to the TARDIS, and while the Doctor offers to save Davros, he refuses, calling the Doctor the "Destroyer of Worlds". The Crucible is destroyed.

The Doctor enlists the help of the other companions, making contact with the Torchwood base, and with Luke Smith, Mr. Smith and K-9, help use the TARDIS to return the Earth to its proper place. Sarah Jane says her goodbyes, as well as Jack, Martha, and Mickey, who has decided to stay in this universe. Using a retroactively closing rift, the Doctor returns Rose and Jackie to the alternate dimension and leaves the new Doctor with her, as he will now grow old with Rose, no longer able to regenerate due to the human influence. Rose asks both Doctors the words that the Doctor was unable to say to her when they last parted (DW: Doomsday). The human doctor, having the same memories and feelings as the proper Doctor, whispers into Rose's ear (most likely telling her that he loves her), and they kiss.

Returning to their universe, Donna finds she begins to have trouble thinking; the Doctor explains that the human mind cannot take in the Time Lord mental abilities. To save her, he wipes her mind of all her encounters with the Doctor, returning her home and explaining to her family, Sylvia Noble and Wilfred Mott, that she must never be reminded of her time with the Doctor or else she will die. As Donna recovers consciousness, she shows no interest in the Doctor; he leaves, though Wilfred promises he will look out for the Doctor every night while he looks at the sky. The Doctor then returns to the TARDIS alone.

Cast

 * The Doctor - David Tennant
 * Donna Noble - Catherine Tate
 * Rose Tyler - Billie Piper
 * Martha Jones - Freema Agyeman
 * Captain Jack Harkness - John Barrowman
 * Sarah Jane Smith - Elisabeth Sladen
 * Clone Doctor - David Tennant
 * Mickey Smith - Noel Clarke
 * Jackie Tyler - Camille Coduri
 * Luke Smith - Thomas Knight
 * Gwen Cooper - Eve Myles
 * Ianto Jones - Gareth David-Lloyd
 * Wilfred Mott - Bernard Cribbins
 * Sylvia Noble - Jacqueline King
 * Francine Jones - Adjoa Andoh
 * Davros - Julian Bleach
 * Dalek Voice - Nicholas Briggs
 * Voice of Mr Smith - Alexander Armstrong
 * Voice of K-9 - John Leeson
 * German Woman - Valda Aviks
 * Scared Woman - Shobu Kapoor
 * Anna Zhou - Elizabeth Tan
 * Liberian Man - Michael Price

Production crew

 * Dalek Operators - Barnaby Edwards, Nicholas Pegg, David Hankinson, Anthony Spargo, Gethin Jones

Individuals

 * Those shown in flashback who died for the Doctor are Harriet Jones, Jabe, The Controller, Lynda Moss, Robert MacLeish, Mrs Moore, Colin Skinner, Bridget Sinclair, Ursula Blake (who did not die because The Doctor was able to bring her back to life), Face of Boe, Chantho, Astrid Peth, Luke Rattigan, Jenny (who is in fact not dead, but the Doctor is unaware of this), River Song and the Hostess.
 * Both Rose and the Doctor recognise the familiar resemblance between Gwen Cooper and Gwyneth (who they encountered in Cardiff in 1869).
 * Rose and Mickey, who previously had an on again, off again relationship, appear to have drifted apart. They do not look at each other, speak to each other, or interact at all, even when they are in the TARDIS together. Mickey does not say goodbye to her (though he does say goodbye to Jackie saying he'll miss her "more than anyone") and he tells the Doctor there's nothing for him in the parallel world, "certainly not Rose".
 * Mickey and Jack's initial dislike of each other appears to have been overcome by both men, possibly due to Mickey's growth into a more mature and capable individual.
 * Just before the Doctor is forced to erase her memory, Donna expresses a desire to meet Charlie Chaplin. This is the second finale in a row to have a character state a desire to meet a famous 20th century personality; previously the Doctor told Martha he wanted to meet Agatha Christie (DW: Last of the Time Lords); Christie subsequently appeared in The Unicorn and the Wasp; it remains to be seen if Donna's reference also serves a foreshadowing. As her mind begins to melt down, Donna also references the American comic strip character Charlie Brown.
 * After parting company with the Doctor, Jack mentions to Martha that he is unsure about UNIT these days and that perhaps Martha could be doing something else. This may be a reference to their earlier adventures with Torchwood. This may also foreshadow Martha's return to that organization. Mickey joins up with the duo, setting up a possible appearance of the character in Torchwood as well.
 * The only one of the current series companions who does ot appear in this episode is Adam Mitchell, possibly because the adventure takes place at a point in time in Mitchell's life before he met the Doctor. His status as a disgraced companion might also have led the writers to exclude him from the story.
 * Like Mickey, Jackie seems to have matured considerably during her stay in the alternate universe. She expertly shoots down a Dalek with a large gun, walks into captivity with little hesitation and expresses sorrow and compassion for a woman she barely met.

TARDISes

 * This is the first episode where the TARDIS is fully-staffed with six pilots, and the first time it is noted definitively that it was designed for six, after various mentions about it being made for more than a single Time Lord.

Technology

 * The purpose of the Osterhagen key is revealed in this episode.  Martha's key is one of several required to set off a network of nuclear weapons buried deep beneath the Earth's surface.  If detonated, these weapons would trigger the explosion of the Earth.  Each key must be inserted into a control panel at an "Osterhagen station". There are apparently five around the world, but only three need to be manned with a key to initiate the detonation.  Locations seen on screen are Germany, Liberia and China.  The "Osterhagen Project"  appears to have been in place for decades, according to the German Woman who supplied food to the guards at the German station.  Given the age of the German Woman, and her claim that she knew of the Osterhagen key when she was in London during her youth, the "Osterhagen Project" likely dates to the days when the Brigadier was in charge of the British arm of UNIT.
 * The technology used to emplace the nuclear weapons at the Earth's crust could therefore be linked to the drilling project featured in DW: Inferno''.


 * The Daleks have access to transmat technology.
 * The TARDIS is captured by the Daleks in what they call a temporal prison but what the Doctor calls a chronon loop.
 * Toshiko Sato installed a time lock around The Hub at Torchwood Three.
 * Sarah Jane uses her sonic lipstick in the same manner as the Doctor's sonic screwdriver. This is the tool's first appearance in the main series.
 * The "three Doctors" send the planets back to their original position through the use of a "magnetron". It is unclear if this is an intentional reference to the magnetrons seen previously in the original series (DW: Day of the Daleks, The Mysterious Planet), or just a general reference to real life magnetrons, used to power microwaves, radar screens and televisions.

Story notes

 * Blue Peter presenter Gethin Jones operates a Dalek in this episode, returning to Doctor Who since his brief appearance as a Cybus Cyberman in The Age of Steel.
 * This was the longest series finale at 65 minutes long, longer even than most of the Christmas specials, except for Voyage of the Damned, which was 71 minutes.
 * Dalek Caan refers to the Doctor as a 'threefold man'. The meaning becomes clear in this episode with both the copy of the Doctor and 'Doctor-Donna'.
 * This episode marks the first series finale to show a preview of the upcoming Christmas Special (2008). After the credits the Cybermen are said to return in the episode. However the episode is unique for being the only series finale in the Russell T Davies era which doesn't end on a cliffhanger. It also breaks the pattern set by the previous two series by not having the Doctor exclaiming "What? What? What?" at the end. In fact it is the only finale scene of the Davies era in which no dialogue is spoken at all.
 * Graeme Harper's penchant for including a distorted image of a main character is present in this story.  Though not included in  every single story he's directed for BBC Wales, it's seen often enough to be considered something of a directorial "signature".  Similar distortion is achieved through the use of  magnifying glasses in Army of Ghosts, The Unicorn and the Wasp, and Utopia,  and with mirrors in Turn Left.   This time, it's Mickey, Jackie and Sarah Jane that get "the Harper treatment" under a curved window.
 * This episode tells us that Harriet Jones, former Prime Minister, actually died in the previous episode.
 * Davros named the Doctor 'The Destroyer of Worlds', which may be a reference to Fires of Pompeii when it was said the Doctor's name was sealed in the Cascade of Medusa herself or to the Doctor being the Ka Faraq Gatri.
 * The Osterhagen key would destroy the Earth. The word, Osterhagen, is an anagram of the phrase, Earth's gone.
 * This story augments the notion that Time Lords have some measure of control over the regenerative process. as seen in Last of the Time Lords.  In truth, most regenerations have added at least a little to the general mythos about the process.  From the notion that a particular physiognomy could be imposed upon the Second Doctor in The War Games, details have been added about how the process works almost every time one has been depicted.  In this case, writer Russell T Davies builds upon his earlier idea that a Time Lord can re-grow whole body parts during "the first 15 hours" following a regeneration (The Christmas Invasion)   Here he suggests that a Time Lord can stop the process prior to entering the final stage, provided that he has a matching genetic receptacle into which he can store the energy.
 * After the hand grows into a new doctor Donna notes that the clone doctor is naked. However careful frame by frame analysis of the scene shows that he (the actor) is actually wearing shorts.
 * When the newly created Doctor discovers he's "part Time Lord, part human" he is shocked and refuses to admit it, meaning he has never been a half-human, though Eighth Doctor said so in the TV Movie. This has confirmed Doctor Who's official website.
 * The scene where the Daleks are speaking German is possibly a tongue-in-cheek reference to the fact that Terry Nation based the Daleks on the Nazis.
 * The word "Exterminieren", which the German Daleks use, is not in common use. In the German dubs of the episodes, the word used in "vernichten" literally, "Reduce to nothing"; colloquially, "Destroy"). The full dialogue for the German Daleks is as follows: "Exterminieren! Exterminieren! Halt! Sonst werden wir Sie exterminieren! Sie sind jetzt ein Gefangener der Daleks! Exterminieren! Exterminieren!" This translates as: "Exterminate! Exterminate! Stop! Or you will be exterminated. You are a prisoner of the Daleks. Exterminate! Exterminate!"
 * This marks the departure of Catherine Tate (Donna Noble) and Billie Piper (Rose Tyler). In an interview with Doctor Who Magazine, Piper was quoted as saying she doesn't see this as a permanent depature. Catherine Tate has no plans to return at the moment, but she has not ruled out a return in the future. Elizabeth Sladen, however, in an interview published after the episode was broadcast, said she doesn't expect to appear on Doctor Who again, although her own spinoff, The Sarah Jane Adventures will continue.
 * The story elements surrounding the destruction of the universe have some casual similarity to ideas found in Life, the Universe and Everything, a Hitch-Hiker's Guide to the Galaxy sequel penned by former Doctor Who script editor, Douglas Adams. Everything was in turn based on an abandoned Fourth Doctor television serial had written, called Doctor Who and the Krikkitmen.
 * This is the third season finale of four to have a character in the TARDIS speaking about possible places to visit before the unexpected departure of a character. In The Parting of the Ways it's the Ninth Doctor speaking of places like the planet Barcelona before regenerating; in Last of the Time Lords, the Doctor suggests visiting Agatha Christie (among others) before Martha announces her departure; in this episode, Donna speaks of visiting Felspoon and meeting Charlie Chaplin before her mind overloads. The only episode to break this pattern so far is Doomsday.
 * As noted in Continuity, below, the Doctor says he's "fine" after leaving Donna, which references an earlier episode (Forest of the Dead) that established that such statements really mean he's not fine at all. Coincidentally, a week after Journey's End first aired in the UK, a Canadian crime drama TV series, Flashpoint, debuted in Canada and the US, and a major plot element of the first episode deals with a police sniper using "I'm fine" frequently in his reaction to having killed a man; as with Doctor Who it is established that the statement can mean the opposite.
 * When the Earth was being towed back to the Sol system, the Ood's song from Planet of the Ood is playing.
 * Jack has flirted with or shown interest in all of the Doctor's companions appearing in this episode save Donna and Jackie. While he may currently consider Jackie off-limits because of her marriage and her connection to Rose, it is interesting to note that Jack does not pursue the two women who have exhibited the most aggressive attitudes towards the opposite sex, and who would arguably be the most likely to return his advances.

Ratings
Journey's End was viewed by 10.57 million viewers in its first airing. This placed it as the No. 1 program of the week, beating the Wimbledon finals and episodes of Coronation Street and Eastenders. This makes Journey's End' the highest rated episode in the 45-year history of Doctor Who, surpassing Voyage of the Damned and The Stolen Earth, both of which ranked second in their respective weeks. However, the episode is not the most-watched episode of the revived series; that distinction belongs to the 13.31 million viewers obtained by Voyage of the Damned (the most-watched episode of all time remains The Ark in Space Part 2 with 13.60 million viewers in 1975, although it only ranked 5th for the week it aired). The episode also achieved an Appreciation Index rating of 91, tieing with The Stolen Earth, a number considered unprecedented for a mainstream network drama production.

Myths and rumours

 * The week between the cliffhanger ending of The Stolen Earth and the broadcast of Journey's End included some of the most intense fan speculation and media attention in franchise history. The significance of the cliffhanger, which appeared to show the Doctor regenerating, along with previously reported speculation regarding Donna and other characters led to many speculations being circulated on fan discussion boards and the media. Among some of the most notable:
 * That David Tennant was in fact leaving the series, and that leaked photos and other information regarding him being in the 2008 Christmas special (as well as media reports the preceding week that he was negotiating to return in 2010) were either a "red herring" or that the Christmas special was to include a flashback.
 * The true nature of Donna was the subject of much speculation, with some fans suggesting her to actually be The Rani or Romana living under the influence of a Chameleon Arch, or a manifestation of the Master.
 * Concerning Donna's ring, at the end of the season 4 finale, when the Doctor says good-bye to her it glimmers briefly into the camera. Some fans theorise that the ring is a possible Chamelon Arch containing Donna's memories of her time with the Doctor. It has also been suggested that the ring resembles a ring worn by The Master in a previous episode. Others theorise that the ring is just large, black, and very shiny.
 * And the prediction that a companion would die led some to believe Donna, Martha or Rose would be the ones destined to die (since it had already been reported that John Barrowman would be returning to Torchwood and Elisabeth Sladen to The Sarah Jane Adventures, ruling out their characters' demise.)


 * The appearance of K-9 was a surprise to many as it had been previously reported that the character would not be appearing in the episode, given the fact the rights to the character are currently held by another party for the planned K-9 television series.
 * After Eve Myles, who had played Gwyneth in The Unquiet Dead was cast as Gwen Cooper in Torchwood, Russell T Davies stated in an interview in Doctor Who Magazine that the characters were unrelated. In this episode, however, Davies reversed this opinion by inserting dialogue strongly implying the two shared common ancestry.  'Not related' and 'unrelated' do no mean the same thing. He did not mean the characters didn't have a similar ancestry, just that their character story lines had nothing to do with each other.
 * There is a possibility that either The Doctor or his twin left behind on Pete's World will eventually manfiest into The Valeyard due to the escalation of pain and abandoment felt each by the other for different reasons. Doubtful that THE Doctor could become the Valeyard but possible that the twin will.(Impossible as Gallifery is destroyed and that the Sixth Doctor's trial happens before the Time War. Yet it could be possible that he will try like Dalek Caan and fly through the Time War and appear as the Valeyard before the Master.) The Valeyard was a side-effect of the doctor's future twelth regeneration. And clearly the human-doctor cannot regenerate.
 * It was strongly believed that Harriet Jones was wanting revenge upon the Doctor for bringing down her reign as Prime Minister, so she decided to help bring the Daleks back, and she was in fact the Supreme Dalek. A supposed "leaked script" showed that Harriet Jones was in fact helping the Daleks. This was proved false.
 * The fact that Jack, Martha and Mickey depart together has sparked speculation that Martha and Mickey may appear in Torchwood, possibly replacing Tosh and Owen.

Discontinuity, Plot Holes, Errors

 * If the TARDIS's power has gone, how does the monitor screen work? Strictly speaking, its power wasn't "gone"; the TARDIS was merely in a temporal prison. While this shut down most power, it clearly didn't cut everything
 * Wouldn't the nuclear warheads placed under the crust have melted? UNIT would most likely have thought about this, and provided some sort of way to protect them.
 * Why did Martha have to travel to Germany to activate the Osterhagen key when the other soldiers were in pods in their home countries? The main pod was in Germany - Martha states that she is in Osterhagen 1. This is supported by the fact the key carries a German name. Also, the five pods were strategically placed around the globe, possibly increasing the chance that a UNIT member could reach them during a crisis.
 * If the act of temporal shifting back to the Time War showed Dalek Caan the entire history of the Dalek race and led him to conclude the Daleks should be destroyed, why didn't he just let Davros die in the war and then kill himself? Caan was driven insane after saving Davros, therefore he had only seen the whole of time after Davros was already safe. He then began setting the course of events that would lead to the fall of the New Dalek Empire.
 * If any mention of the Doctor or the TARDIS would cause the Time Lord consciousness within Donna to reawaken and burn up her mind, isn't the Doctor taking a tremendous risk by letting Donna see him in the Nobles' house? Maybe The Doctor wishes to test the effectiveness of the memory wipe and also determine whether there are any negative effects on her. According to Phil Collinson and Julie Gardner in the commentary podcast, a scene filmed but cut showed Donna reacting to the sound of the TARDIS dematerializing and then dismissing it.
 * If Mickey Smith was allowed to stay on the normal Earth, why did Rose and Jackie have to go back? After all, the Doctor could have brought Pete back as well, and their child. The Doctor wanted to keep the second Doctor sealed off in the parallel world where he couldn't cause any trouble, and wanted Rose to look after him. The episode also indicates that there is only a limited amount of time for the TARDIS to remain on Pete's World, not enough time to round everyone up. Also, both Pete and the young son were born on Pete's World; it wouldn't have been fair to force them to leave their homeworld. There is no indication of Jackie requesting to stay on her original world.
 * With all of her memories since The Runaway Bride erased, wouldn't Donna realise that she has lost about a year and a half of of her life, and shouldn't she think it's her wedding day? But the Doctor states that he erased memories of him and the TARDIS, meaning that he never erased 2 full years of her life. She presumably remembers a mundane version of that time, and will naturally dismiss any gaps.
 * If the Osterhagen key and its associated doomsday device had been around for years, why wasn't it activated during the events of Doomsday or, more to the point, The Year That Never Was (DW: Last of the Time Lords)? ''The Master used the archangel network to crush resistance. It's also probable that as the Master not only became Prime Minister, but also was involved with the top-secret weapon deployed against the Sycorax, that he was aware of the Key and took steps to prevent its use. Also with the Doctor around in Doomsday, they didn't need to use the key, as they would only need a last resort when the Doctor was completely helpless and couldn't stop it (it's a last resort weapon.)
 * How did the Daleks get Jack into the trash container? Presumably they levitated him using the same technology that allows Daleks to fly.
 * Sarah-Jane and Mickey somehow get through a hallway, up the stairs, open a door and close it (twice) despite the fact a) the Dalek looking at the old woman could have easily seen them, b) Behind the party are dozens of daleks, c) It's probably on sec. cam, and D), just as Sarah Jane convinces Mickey not to go out, a Dalek passes by.
 * Jack is in a furnace for 10 seconds and nothing happens to his clothes. In previous episodes of both 'Doctor Who' and 'Torchwood', Jack's clothing appears to survive his many violent deaths. Considering he's generally depicted wearing the same outfit since World War II, it's not surprising his clothing is intact, even if it is somewhat unbelievable. Consider also the continuity, story pacing and possible censorship problems if Jack's clothing were damaged or destroyed every time he died. Also it was stated in the fear forcast that one of them said "One naked person is enogh" as the clone Doctor had no cloths
 * Why did Davros bother getting habited planets along with uninhabited planets? Surely it's less bother than just sitting back and do nothing. It can be claimed it was for the tests, but why get more than one? Also it can surely be used on animals? Construction of the Reality Bomb required twenty-seven specific planets that automatically aligned themselves to the proper configuration. As such, Earth and the other inhabited worlds that were captured were necessary to the plan. As far as subjugating Earth and using humans as test subjects, it is likely that Earth, the home of UNIT, Torchwood, and Sarah Jane Smith, posed the most serious threat out of all the planets captured. In addition, conquering the Earth and using humans may have been a form of revenge against the Doctor.
 * Tardis drags Earth faster than light across the Universe, few ornaments fall off walls, nuff said. This can be explained by the in-story physics established in the show. Indeed, FTL travel and rapid acceleration without devastating g-force effects are a staple of almost every modern science-fiction film or series. If the TARDIS can somehow generate enough power to move a planet, creating an 'inertial dampening field' (as in Star Trek) big enough to affect the whole planet should not be an issue.
 * The science of complete universal destruction is very bad. Somehow the reality bomb (which is not a bomb, but a gun) can, despite moving very slowly in the tests, a)be implied to take everything out in no time at all and b) every Universe. This is SCIENCE FICTION. It doesn't have to make perfect sense. This is where the Medusa Cascade space-time rift comes in.
 * In Turn left when the stars are going out, doesn't that mean the reality bomb is already on the loose? It can be claimed the reality was reversed so it never happened, but how could Rose predict it, unless she saw it in her, or another universe? As the Doctor has stated before, it is often possible to see the effect before realizing the source. Perhaps the removal of the Reality Bomb rewrote the histories of all the other universes, eliminating the possibility that they would be destroyed. As long as the potential for the bomb existed, then it would be possible to see its effects in other timelines.
 * Rose clearly doesn't know Jack is immortal even though in Turn left she has full knowledge of torchwood and implies Jacks imortality with 'Captain Jack Harkness has been transported to the Sontaran homeworld' It is never clearly stated how much Rose knows about Torchwood Three, specifically the Torchwood that exists in her home universe. She works for the Torchwood in the alternate universe, and while she may be aware that Jack was transported to Sontar in Donna's pocket universe, she did not necessarily know that his immortality was the reason.

Continuity

 * When the Doctor sees Gwen Cooper for the first time, he asks if she comes from a long line of family from Cardiff. This is because of the similarity between Gwen and Gwyneth (DW: The Unquiet Dead), both of whom are played by Eve Myles. The Doctor and Rose both recognize the uncanny family resemblance.
 * This is the first occurrence of the Doctor's TARDIS being piloted by six people, that number first being specified in NA: Cat's Cradle: Time's Crucible.
 * This episode marks the last appearance of the Tenth Doctor's severed hand which first appeared in DW: The Christmas Invasion and throughout the first season of Torchwood.
 * Davros mentions meeting Sarah at the birth of his creations; this happened in DW: Genesis of the Daleks.
 * Mickey Smith and Jackie Tyler last appeared in DW: Doomsday.
 * Donna tells the Doctor how to fix the Chameleon Circuit which has been broken since DW: An Unearthly Child. The Sixth Doctor had previously attempted this in DW: Attack of the Cybermen, as had the Fourth Doctor in DW: Logopolis.
 * This is the fourth time a Doctor has been depicted in a way to suggest he was unclothed. The first time was in Spearhead from Space in which a newly regenerated Third Doctor took a shower. The second was during the regeneration from the Seventh to the Eighth Doctor, where he was merely covered by a sheet. The Ninth Doctor appeared shirtless during the torture scene in Dalek.
 * Gallifrey is mentioned again and the first time it has been mentioned in an episode with Rose Tyler.
 * The Doctor tells Wilf that he's "fine" after he drops off Donna. This echoes a similar statement in Forest of the Dead which Donna interprets as meaning the complete opposite.
 * The Verron Soothsayer, who gave Sarah Jane Smith the Warp star, was mentioned previously in SJA: Whatever Happened to Sarah Jane?

DVD and Other releases

 * This episode will be released as part of Series 4 Volume 4 DVD alongside Turn Left and The Stolen Earth on 1st September 2008.
 * It will also be released in the Series 4 boxset on 3 November 2008.