After a number of extremely brutal adventures for the Doctor, "Partners in Crime" signals a deliberate change in tone. He's clearly carrying a lot of guilt for everything that happened with Martha, and missing Rose (or indeed anyone to share the TARDIS with), and relishes the company of a Donna Noble who appears to have been entirely changed by his appearance in her life, but in her case, the influence has been entirely to the good.

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

(The episode is available on iTunes and Amazon.)

Russell T Davies had originally intended for the Doctor's next companion to be a thirty-something called Penny Carter, who would have been rather bossy and nursing the heartache of a recent break-up. The character was based partly on Catherine Tate's Donna Noble, from "The Runaway Bride," and as it turned out, Catherine was interested in making a return to the show. In this story, Penny Carter is the name of the journalist investigating Adipose Industries, a character whose primary role is to make Donna look good, and reinforce the idea that the Doctor chooses his companions most carefully. This is further underlined when Donna says of Penny, "some people just can't take it."

Russell T Davies wanted to base the story around cosmetic surgery, originally considering some form of alien infection from Botox injections, that would cause victims to transform into hideous monsters.

He also looked at the idea of an invasion of thousands of terrifying canine aliens called Vorlax, who would come to Earth via a portal in an abandoned house in London. A previous plan of capturing an area of London under a huge dome (similar to the plot of The Simpsons movie) was later transferred to "The Sontaran Stratagem," albeit on a more global scale.

While Davies says he based the character of Miss Foster on Supernanny / Family S.O.S. star Jo Frost and Argentine politician Eva Perón, Sarah Lancashire (who plays her) considered the character to be more of a malevolent Mary Poppins.

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

The appearance of the Adipose (named after adipose tissue, the proper name for body fat) was based on a stuffed toy belonging to Davies, but he also wanted them to look like cute blocks of lard, along the lines of the Pillsbury Doughboy but less human shaped. Post-production agency The Mill added the sole tooth and the ears, to make them even cuter.

The scene where the Doctor and Donna are both investigating Adipose Industries but entirely fail to bump into one another was exceptionally tricky, as both actors had to clearly be unable to spot the other throughout. It ran to 30 takes. By contrast, this glorious scene, when they finally do clap eyes on each other, was largely improvised. The script demanded that Donna act out this series of messages: "I came here, trouble, read about it, internet, I thought, trouble = you! And this place is weird! Pills! So I hid. Back there. Crept along. Looked. You. Cos they..."

In the event, Tate simplified it a little, improvising the conversation like this:

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

If you look at the taxi that comes to pick up Stacey Campbell, the woman who has just been absorbed by the Adipose, you'll see an ATMOS sticker on the windscreen, a subtle nod ahead to "The Sontaran Stratagem" / "The Poison Sky."

The scene in which Billie Piper makes her unexpected reappearance as Rose Tyler was edited out of any press preview showings of the episode, so that it would be a treat for fans.

While the Adipose spaceship is overhead, causing widespread public panic, Wilfred Mott is entertaining himself by listening to Dusty Springfield's version of "Twenty-Four Hours from Tulsa":

https://www.youtube.com/watch?v=7Q9DSFu6eCQ

One of the more upsetting aspects of this story's production came when Howard Attfield, who had played Donna Noble's father Geoff in "The Runaway Bride" revealed he would be unable to reprise the role for the rest of the season, having shot many of the scenes for this story already, as he was receiving chemotherapy, and had also just broken his leg. The team contacted Bernard Cribbins, who had just played the newsvendor (who was called Stan Mott at the time) in "Voyage of the Damned" to see if he would appear as Donna's grandfather, taking on Geoff's scenes under the name Wilfred. Having secured his approval on October 15, 2007, they had time to change the end credits of "Voyage of the Damned" so Wilfred appeared to have been a planned addition to the cast from the start.

Attfield died in October 31st, 2007, and this episode was dedicated to him.

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