"The Doctor's Daughter" takes an artful approach to the classic Doctor Who stories in which the TARDIS arrives in the middle of a conflict and the Doctor has to deal with one army while his companion is captured and has to deal with the opposing forces. This time, he has to face part of his past that we've never really seen that much of, his resolve around guns is sorely tested, and he is gently chided by Donna Noble into accepting that there might be room in his battle-scarred heart for more than one friend at a time.

Here are a few things that you should keep an eye out for, the next time you watch.

(The episode is available on Amazon and iTunes.)

The germ of inspiration for this story lies with an interview writer Stephen Greenhorn ("The Lazarus Experiment") gave to Doctor Who Magazine, in which he said the Doctor tended not to change as a character. This inspired Russell T Davies to suggest a script in which the Doctor's attitude and values are challenged by someone for whom he is not necessarily an alien. Someone, in fact, who is genetically related to him, but who knows none of his history.

This is one of the few episodes in which the Doctor makes explicit reference to his family. While the First Doctor traveled with his granddaughter Susan, her parents were never mentioned, or grandparents. The Ninth Doctor does hint that his family followed those lines in "The Empty Child." Dr. Constantine says, "Before the war, I was both a father and a grandfather," and the Doctor replies, "I know the feeling." He also mentions having had a brother, in "Smith and Jones," and said "I was a dad once" in "Fear Her."

https://www.youtube.com/watch?v=PBFflbA5Bkk

While it might seem exceptionally fitting that Georgia Moffett—actual daughter of Fifth Doctor Peter Davison—should be playing the Doctor's daughter, this wasn't planned. In fact Georgia had already auditioned for the part of Robina Redmond in "The Unicorn and the Wasp," and had she got the part, she wouldn't have been able to play Jenny. Although, Davison told Doctor Who Confidential that, as soon as he completed filming the Fifth Doctor / Tenth Doctor meeting "Time Crash," he said to Georgia "[now] it's your turn".

Georgia had already appeared beside her (real) dad for the Doctor Who Big Finish audio story "Red Dawn" and in the comedy series Fear, Stress & Anger:

https://www.youtube.com/watch?v=w0gmacEWegw

The location shoot for the Hath camp, which took place in the Marble Room at Cardiff City Hall, was interrupted due to a protest outside the building, concerning school closures. Several shots had to be postponed for a few days.

The human soldiers in this story were originally called Takrans, but this was abandoned due to confusion over how to pronounce the word.

Although the Hath communicate silently, with bubbling liquid across their mouths, Greenhorn wrote all of their dialogue, so the actors behind the masks would know how to react. The two principal Hath in the story were named Hath Peck (after Gregory Peck) and Hath Gable, after Clark Gable.

As the Doctor and Donna come across the bounteous greenery around the Source, Donna asks, "So why are we suddenly in Kew Gardens?" Kew is a well known botanical gardens and tourist destination in London, although this part of the episode was actually filmed in Plantasia, a large public hothouse in Swansea.

Russell T Davies had originally planned to kill Jenny off, in order to further underline the loneliness of the Doctor. But he changed his mind after a discussion with Steven Moffat. Steven has also said (in the book Doctor Who: Companions and Allies) that Jenny's resurrection came from the Source, not from her Time Lord genetic code.

And finally, did you know that Jenny's acrobatics, in order to get past all of those laser beams...

https://www.youtube.com/watch?v=VjO_GAN1BCc

... were inspired by the video for "Toxic" by Britney Spears?

https://www.youtube.com/watch?v=LOZuxwVk7TU

NEXT: 10 Things You May Not Know About ‘The Unicorn and the Wasp’

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