The title of episode 1, "The Stolen Earth", of this two part story was withheld until two weeks before broadcast, as, according to Executive Producers Russell T Davies, ‘it gives away too much’.

This story marks the first appearance of a ‘starring’ caption after the opening credits, listing Penelope Wilton, Adjoa Andoh, Eve Myles and Gareth David-Lloyd.

This story features the return of many past characters, including five companions and the recurring villain Davros, his first television appearance since the 1988 Seventh Doctor story "Remembrance of the Daleks". Julian Bleach, who plays Davros, appeared as the "Ghostmaker" in the Torchwood episode "From Out of the Rain". Davros has been referenced twice since the series restarted in 2005, but never by name. He was referred to in the 2005's story "Dalek" as a ‘man who was king of his own little world’ and in "Daleks in Manhattan/Evolution of the Daleks" as the creator ‘who removed emotion to make them stronger’.

Freema Agyeman reprises her role as Martha Jones for the second time in the series, and John Barrowman and Elisabeth Sladen return as Jack Harkness and Sarah Jane Smith. Unlike in Sladen's last Doctor Who appearance, "School Reunion", she receives credit in the opening titles. Adjoa Andoh returns as Francine Jones for the first time since "The Sound of Drums/Last of the Time Lords", while Penelope Wilton reprises the role of Harriet Jones, last seen in "The Christmas Invasion".

Michael Brandon (who plays the part of General Sanchez) is probably best known for his portrayal of tough 80's New York cop Lt. James Dempsey in the 1980s television show Dempsey and Makepeace.

Kelly Hunter (who plays the Shadow Architect) appeared in the BBC's 2005 adaptation of Bleak House alongside Carey Mulligan, who played Sally Sparrow in the 2007's story "Blink".

This story marks the first crossover with spin-off series Torchwood and The Sarah Jane Adventures with Gwen Cooper (Eve Myles - who previously played Gwyneth in the 2005 Doctor Who episode "The Unquiet Dead"), Ianto Jones (Gareth David-Lloyd), Luke Smith (Thomas Knight), and Mr Smith (Alexander Armstrong) starring. There are also several mention of events within those respective series. Sarah Jane's encounter with The Slitheen, seen in The Sarah Jane Adventures stories "Revenge of the Slitheen" and "The Lost Boy", is mentioned by Captain Jack. Similarly, the events of Torchwood episode "Exit Wounds" and the deaths of Torchwood personnel Toshiko Sato and Owen Harper are alluded to by Gwen Cooper and Ianto Jones in the face of what they feel is imminent death. Sarah Jane Smith and Torchwood characters Maria Jackson, Alan Jackson, Clyde Langer and Rhys Williams are all referenced.

Jason Mohammad reprises his role as the newsreader from "Turn Left", and Lachele Carl also reappears as the recurring American newsreader from Doctor Who and The Sarah Jane Adventures, credited as "Trinity Wells". Dalek Caan also returns in this episode for the first time since "Daleks in Manhattan/Evolution of the Daleks", along with the Judoon from "Smith and Jones". Television host Paul O'Grady and biologist Richard Dawkins also appear as themselves in brief scenes - continuing the pattern of celebrity appearances in the final story of every series since the show's revival in 2005.

This isn't the first time Bernard Cribbins has faced the Daleks. He originally starred in the 1960s feature film "Daleks: Invasion Earth 2150 AD" as policemen Tom Campbell. The film, starring Peter Cushing as The Doctor, was based on the 1964 First Doctor story "The Dalek Invasion of Earth". The Supreme Dalek's red colour scheme is a nod to the Dalek Controller from these two Dalek films.

This story marks the first on-screen appearance of the Shadow Proclamation, first mentioned in "Rose", and the Medusa Cascade, which was first mentioned in "The Sound of Drums/Last of the Time Lords". The Judoon debuted in the 2007's story "Smith and Jones". Donna mentions that 'the bees have disappeared', an occurrence seeded in several stories in this season including "Partners in Crime", "Planet of the Ood", "The Unicorn and the Wasp" and "Turn Left", whilst the events of "Turn Left" as a whole are also referenced when the servant at the Shadow Proclamation mentions to Donna that there had been "something on her back". The regeneration effect seen here is the same style used in "Bad Wolf/The Parting of the Ways" and "Utopia", where the Ninth Doctor and The Master regenerated respectively.

Among the planets that have been stolen are Callufrax Minor, Woman Wept, Clom, Adipose 3, Pyrovilia and the Lost Moon of Poosh – mentioned in "The Pirate Planet", "Boom Town", "Love & Monsters", "Partners in Crime", "The Fires of Pompeii", and "Midnight" respectively. The latter story is referenced by Wilfred Mott, who mentions Donna phoning from the diamond planet Midnight. The Doctor theorizes how the lost planets were taken asking Donna if there were electrical storms or freak weather before she left Earth; these symptoms are the symptoms of an imminent H2O scoop as seen in "Smith and Jones". Pushing something out of sync with the rest of time, as is done with the stolen planets, is also used by the Sontarans to disguise the alien technology in the ATMOS devices in "The Sontaran Stratagem/The Poison Sky".

The Doctor says ‘Someone tried to move the Earth once before. A long time ago’. This is possibly a reference to either 1964 First Doctor story "The Dalek Invasion of Earth", in which the Daleks tried to move the Earth but their attempts to pilot the planet were thwarted by the pull of the Earth's magnetic core, or the 1986 story "The Trial of a Time Lord" where the Earth was moved as part of a shady cover-up by The Time Lords.

Also mentioned in this story is Mr. Copper, a character who appeared in "Voyage of the Damned", as the inventor of the sub-wave network.

The airborne aircraft carrier Valiant, which last appeared in "The Sontaran Stratagem/The Poison Sky", also appears, and is apparently destroyed by the Daleks.

The gun Captain Jack uses near the end of the episode is the gun he created from the Defabricator, previously seen in "Bad Wolf/Parting of the Ways".

This isn't the first time milkmen have featured in the series - the Third Doctor disguised himself as one to break into Global Chemicals during 1973's "The Green Death" and a milkman was attacked by a Cheetah Person at the start of 1988's "Survival".

Despite their many encounters, The Doctor has only been shot by a Dalek twice before: in 1973's "Planet of the Daleks" (when a Dalek deliberately disabled the Third Doctor by zapping his legs) and in 1975's "Genesis of the Daleks", when, just prior to blowing up the Daleks' incubation room, The Fourth Doctor received a glancing blow to his hand from a Dalek ray.

The proclamation ‘My vision is not impaired!’ by a Dalek when it is unaffected by Wilfred Mott's paintball gun, is a reference to another of the Daleks' famous catchphrases ‘My vision is impaired!’ A Dalek was disabled by obstructing its vision in the very first Dalek story "The Daleks" in 1963.

In the audio commentary for episode 1 of this story, it is mentioned that the Slitheen were originally going to appear at the Shadow Proclamation and voices for them were recorded. It is mentioned that they were probably cut due to time.

At 63 minutes in length the second episode is approximately 20 minutes longer than the standard episodes of the revived series. This episode also marks the final appearance of Donna Noble as the Doctor's companion.

One significant feature of the second episode is the appearance of a second Tenth Doctor. Unlike the multiple incarnations of The Doctor who have appeared in previous stories "The Three Doctors", "The Five Doctors" and "The Two Doctors", this Doctor is identical to the Tenth Doctor and so is played by David Tennant. In Doctor Who Confidential for this episode, Russell T Davies explains ‘This is so busy and so mental and so epic and universal in scale that of course you need two Doctors to solve it’.

The Doctor references his sword fight against the Sycorax leader in "The Christmas Invasion", in which he lost and regrew his hand. Numerous clips from the revived series are used in various flashbacks: when The Doctor thinks about his encounters with Donna and the seeming coincidences that have brought them together, clips are shown from earlier episodes featuring Donna and/or her grandfather Wilfred; when Davros taunts The Doctor about the countless deaths he has caused, clips of various characters who died defending The Doctor are shown, namely Harriet Jones, Jabe, The Controller, Lynda, Sir Robert MacLeish, Mrs Moore, Mr Skinner, Ursula Blake, Bridget, The Face of Boe, Chantho, Astrid Peth, Luke Rattigan, Jenny, River Song and The Hostess; and when The Doctor purges Donna's memories, clips are shown from earlier episodes featuring Donna.

It is sometimes been claimed that TARDISes are designed to be flown by six pilots (e.g. in the 1992 novel "Cats Cradle: Time's Crucible"), although this is the first time this has been confirmed in the television series.

The Doctor also comments on ‘spatial-genetic multiplicity’ regarding the similarities between Torchwood character Gwen Cooper and the maid Gwyneth in the episode "The Unquiet Dead", both of whom are played by Eve Myles.

Two members of the former 'Cult of Skaro' have now seen the Daleks for what they truly are - first there was Dalek Sec, in the 2007 story "Daleks in Manhattan/Evolution of the Daleks", and now Dalek Caan.

Davros recalls seeing Sarah Jane Smith on Skaro, when he first created the Daleks. This is, of course, a nod to the 1975 story "Genesis of the Daleks", in which the Fourth Doctor and Sarah Jane travelled to Skaro in order to stop the Daleks ever being created.

'Osterhagen' is an anagram of 'Earth's Gone'.

For the Dårlig Ulv Stranden ('Bad Wolf Bay') scenes towards the end of episode 2, the production crew returned to the beach at Southerndown, a few miles west of Cardiff. They previously filmed there for Rose Tyler's departure in "Army of Ghosts/Doomsday".

Those of you who have been slightly bothered for the last 12 years by the comment made by the Eighth Doctor in the Television Movie that he was half human on his mother's side, can probably breathe a sigh of relief now. The Second ‘Tenth’ Doctor seems shocked that he has become uniquely half human due to the biological metacrisis with Donna, strongly suggesting that he never was before.

If you were wondering about some of the dialogue during Martha's trip to Germany in episode 2, Script Editor Lindsey Alford and Kevin Myers have provided the following translations: