The TARDIS is drawn to the planet Messaline, depositing the Doctor, Donna and Martha in the midst of a war between human colonists and the piscene Hath which has been waging for generations. Martha is kidnapped by the Hath, while the Doctor and Donna discover that the humans breed by accelerated progenation: recombining a single individual's DNA to produce a new, adult person, ready for battle. Subjected to this process, the Doctor abruptly comes face to face with his daughter, Jenny, even as Donna begins to discover that there is more to the war on Messaline than meets the eye.

Stephen Greenhorn had written The Lazarus Experiment for Doctor Who's 2007 season, and executive producer Russell T Davies was eager to invite Greenhorn back the following year. While preparing for the new season, Davies read an interview that Greenhorn had given to Doctor Who Magazine in which he discussed the way that the Doctor, as a character, is virtually unchanging. This suggested to Davies that Greenhorn should be assigned a script which would challenge this very notion by pairing the Doctor with a character who (by science-fictional means) would in fact be his genetic offspring. However, unlike Susan -- the Doctor's granddaughter who had accompanied him during Doctor Who's first ten serials in 1963 and 1964 -- this new character would initially be conditioned with attitudes very much at odds with the Doctor's.

Greenhorn began working on the script -- given the title The Doctor's Daughter -- from around the start of March 2007. In addition to the basic storyline, Davies asked Greenhorn to include former companion Martha Jones in the episode. Martha would inadvertently rejoin the Doctor in the preceding adventure, The Sontaran Stratagem / The Poison Sky, but would have good reason to want to return home after her experiences in Greenhorn's tale. Other elements -- including the underground war and the Hath's mode of communication via bubbling liquid -- were also suggested by Davies.

The Doctor's Daughter evolved considerably during its development, with various plot points -- such as the war's seven-day length, Donna's investigation of the mysterious numbers, and the greenhouse venue of the climactic scenes -- added to later drafts. The Hath's opponents were originally called the Takrans, but this was excised because of its ambiguous pronunciation. Even though they communicated by gurgling, Greenhorn wrote all of the dialogue for the Hath to give the actors under the masks an impression of how their characters should behave. He also named the two main Hath Peck and Gable, after Hollywood icons Gregory Peck (To Kill A Mockingbird) and Clark Gable (Gone With The Wind).

For a long time, Jenny was meant to die at the end of the story, but writer Steven Moffat -- who was preparing Silence In The Library / Forest Of The Dead for later in the season -- suggested that this was too obvious a denouement, and so the ending was revised to include her revivification. Another late change involved the Doctor threatening to shoot Cobb: originally, he was taken away to be executed instead.

The Doctor's Daughter was paired with Midnight as the sixth block of Doctor Who's 2007-2008 production schedule, which was double-banked with Block Seven (Turn Left). The director assigned to Block Six was Alice Troughton, who had previously worked on many episodes of shows such as Doctors, Holby City and EastEnders. Troughton had also helmed Small Worlds and Out Of Time for the opening season of Torchwood, plus Revenge Of The Slitheen and Eye Of The Gorgon, the first two stories of The Sarah Jane Adventures' initial season.

Troughton's most critical task in preproduction was to cast someone to play Jenny. Ironically, the role ultimately went to Georgia Moffett, the daughter of Peter Davison, who had played the Fifth Doctor. This was not stunt casting: Moffett was an experienced actress, having appeared in programmes such as Peak Practise, The Bill and Where The Heart Is. She had also appeared alongside her father in the 2000 Doctor Who audio play Red Dawn from Big Finish Productions. Despite her heritage, Moffett had not been particularly interested in Doctor Who until her young son, Tyler, became an avid devotee with the series' 2005 revival. Now a Doctor Who fan in her own right, Moffett had auditioned for the role of Robina Redmond in The Unicorn And The Wasp some months earlier.

Work on The Doctor's Daughter began at Upper Boat Studios, where the TARDIS material and the closing sequence of Jenny leaving Messaline were recorded on December 11th. The same day, the BBC announced that Julie Gardner would be leaving her positions as executive producer of Doctor Who and Head of Drama for BBC Wales following the completion of the Doctor Who specials which would air during 2009. She would be replaced by Piers Wenger, who produced the award-winning telefilm Housewife, 49.

On December 12th, the scenes of Martha and Hath Peck on the planet's surface were filmed at the Aberbaiden Open Cast Colliery in Cefn Cribwr near Kenfig. On the 13th, the Marble Room at Cardiff City Hall posed as the Hath encampment. Unfortunately, the location was being picketed due to controversy over school closures. This caused Troughton's team to lose several hours, forcing the postponement of a number of shots.

The next venue was the Celynen Colliers Institute and Memorial Hall in Newbridge, beginning on December 14th and continuing from the 17th to the 19th. All of the scenes at the human encampment were filmed there, and Troughton was also able to complete the rest of the Hath encampment material on the 18th. Partway through work on December 19th, the team moved to the Dupont Building at the Mamhilad Industrial Park in Pontypool. This provided the spaceship corridor, and recording there continued on the 20th. On December 21st, the scenes in the greenhouse were taped at Plantaisia in Swansea.

After the Christmas break, the cast and crew of The Doctor's Daughter reassembled on January 7th, 2008 at the Rhondda Heritage Park in Trehafod near Pontypridd, for the scenes in the tunnel where the Doctor locates the secret panel. The next two days were spent back in the Mamhilad Industrial Park, this time at the Johnsey Estates, recording the material in the tunnel where Jenny disables the laser beams. The sequences in the area where the TARDIS materialises were filmed on January 10th and 11th at the Barry Shooting Range on Barry Island. The last major scene to be completed was Martha's return home, at Mark Street in Cardiff on the 18th. The same day, pick-up shots from the greenhouse sequence were captured at Roath Conservatory in Cardiff. An insert of the toy mouse exploding was filmed at Upper Boat on the 24th.

Meanwhile, it transpired that over the course of making The Doctor's Daughter, an attraction had developed between David Tennant and Georgia Moffett. Soon after finishing the episode, the pair began dating. Moffett was the second Doctor Who guest star to have been romanced by Tennant; a two-year relationship with Sophia Myles, who had played Madame de Pompadour in The Girl In The Fireplace, ended in 2007. Tennant and Moffett were still seeing each other more than a year later.

• Outpost Gallifrey: New Doctor Who Series News Page, edited by Shaun Lyon.
• Doctor Who Magazine Special Edition #20, 19th November 2008, “Episode 6: The Doctor's Daughter” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Writer's Tale by Russell T Davies and Benjamin Cook (2008), BBC Books, ISBN 978 1 846 07571 1.