"Journey's End" is a heroic attempt by Russell T Davies to tie up all the loose ends from four seasons of the relaunched Doctor Who, while still leaving a few nagging questions for future show-runners to address or ignore (such as the whereabouts of Jenny, the Doctor's clone daughter), as they wish.

It is also a chance for the Doctor to once again see the other lives he could be living, were he more of a mortal man and less of a Time Lord, and to witness first hand the kind of devastation involved in trying to be both at once.

Here are a few things to keep an eye out for, the next time you watch:

(The episode is available on Amazon and iTunes.)

One of the factors that particularly complicated this double-length story's fraught conception was Billie Piper's wedding. While working on story ideas, Russell T Davies learned that Billie would be unavailable during the allotted filming block as she would be on honeymoon, and so he amended his story plan so that Rose Tyler only appears at the very end, with the Doctor arriving in the parallel Bad Wolf Bay, and delivering the Metacrisis Doctor to Rose, thereby leaving out Mickey and Jackie Tyler from the story. Thankfully, arrangements were made to move the shooting schedule around, giving us the full Rose Tyler story.

However, Billie Piper's wedding itself, on December 31st, 2007, also took place while Russell T Davies had to finish off writing "The Stolen Earth". And with so many threads to juggle across a changeable schedule, he found himself rushing to complete the script, and couldn't attend the wedding.

One element that didn't make the final shooting script was a long flashback into the early years of Davros, including his early experiences as a young man on Skaro, his scientific experiments on Kaled soldiers that lead to the development of the Daleks, and the disfiguring explosion which left him needing a Dalek wheelchair. Some of this has since been covered in the Season 9 stories "The Magician's Apprentice" / "The Witch's Familiar".

The scene where the Daleks are speaking German, while possibly a nod to Terry Nation's conception of them as interstellar Nazis, contains an interesting moment of international translation. While clearly useful for an English-speaking TV show, the word "Exterminieren!" isn't a commonly used expression, so when the show is broadcast in Germany, the Daleks say either "Eliminieren!" or "Vernichten!" instead, as in this clip from a German-dubbed episode of "Revelation of the Daleks":

https://www.youtube.com/watch?v=VujXTkjxp0c

The famous line said by the Metacrisis Doctor to Rose, when she asks how he would finish the last thing he'd been saying to her when they last met in Bad Wolf Bay, was deliberately intended to be an ambiguous view of what is, ultimately, a private moment. However, executive producer Julie Gardner did state in the Doctor Who Confidential special for "Journey's End" that the Doctor did actually say exactly what you'd imagine he would have.

Another abandoned story idea was that the Doctor would hand the Metacrisis Doctor and Rose an object resembling a piece of coral, which would be a seed from which a new TARDIS could be grown. This was actually filmed, but left out in the final edit, partly to keep things simple, but also because it was felt that TARDISes should be much harder to create than this. There again, Russell T Davies has subsequently said (in The Writer's Tale) that it's fine to assume this happened off camera.

If you've ever felt the final scene, in which a soaked Doctor prowls the TARDIS console room which was so recently full of his friends, was a little downbeat for a season finale, it's intentional. That year's Christmas special "The Next Doctor" was filmed at the end of the filming block for Season 4, which meant the production team could make use of all the speculation around David Tennant's departure (and the regeneration that kicks off "Journey's End") to end the episode with a "next time" montage of clips from a story purporting to show a new Doctor played by David Morrissey.

The intended cliffhanger would have seen the Doctor attacked by Cybermen from within his own TARDIS, as soon as he leaves Donna's house, but Doctor Who Magazine writer Benjamin Cook suggested to Russell T Davies that this would detract from the emotion of the moment.

Another cut scene involved Donna having a brief moment of recognition when the TARDIS dematerialises from outside her house. She's inside the kitchen and hears the noise, and experiences a jolt of deja vu, before continuing her phone conversation. It was felt that this would undermine the life and death permanence of her situation.

https://www.youtube.com/watch?v=1al-pUIpk1s

Davros calls the Doctor "the destroyer of worlds," which echoes a description of the Seventh Doctor, taken from the novelisation of "Remembrance of the Daleks". The book cites an off-screen item of Whovian lore, stating that the Daleks call him Ka Faraq Gatri, which translates as "Bringer of Darkness" or "Destroyer of Worlds".

Having shocked both journalists and the Doctor Who audience with the regeneration cliffhanger at the end of "The Stolen Earth," which had been kept a total secret before broadcast, the production team were delighted to discover that not only was "Journey's End" the most watched episode of Season 4, it was the most watched program in the UK across all channels that week. It beat not only the soap operas Coronation Street, EastEnders and Emmerdale, but the live coverage of Wimbledon.

No episode of Doctor Who had ever been No.1 before, although "Voyage of the Damned" and "The Stolen Earth" were both No.2. The Doctor Who stories with the largest viewing figures (as opposed to being the top rated show during a week's broadcasting) are Voyage of the Damned (13.31 million viewers) from the relaunched show, and part four of "City of Death" (16.1 million).

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