The Doctor takes Donna to the Ood-Sphere in the year 4126. This is the planet where Ood are bred by the Ood Operations company, to be distributed as willing servants to humanity throughout the cosmos. But something is going wrong with the Ood: their eyes are turning red, leading to acts of murder and ultimately a feral state. The search for answers leads the time travellers to uncover the terrible truth behind the origins of the Ood race.

Keith Temple had gotten his start in television by writing for documentaries, before contributing to programmes such as Emmerdale, Casualty, EastEnders and Byker Grove. Temple had been a Doctor Who fan in his youth, and his partner, Morag Bain, had worked with Doctor Who executive producer Russell T Davies on the family series Children's Ward. As a result, Temple was able to forward Davies his script for the forthcoming production Angel Cake. On this basis, during the summer of 2006 Davies invited Temple to discuss the possibility of writing for Doctor Who. Some thought was given to assigning him a slot for the programme's 2007 season, but it was ultimately decided to bring Temple on board for 2008 instead.

Davies had long been keen to revisit the Ood, a servitor race introduced in 2006's The Impossible Planet which had proved popular with the production team and the public alike. Indeed, he had previously considered incorporating the Ood into the 2007 adventure 42. In preparing for the 2008 season, Davies contemplated devoting a two-part slot to an Ood adventure, but ultimately decided that the storyline would work better if it was not overcomplicated. The chief casualty was an extended sequence set in caves beneath the planet's surface, in which the Doctor searches for the giant Ood brain. It was this Ood adventure that Davies offered Temple; entitled Planet Of The Ood, it was intended to be the season's second episode.

Temple was asked to set his adventure on an ice planet, because this was an environment not yet explored since Doctor Who's revival in 2005. It was also suggested that the character of Ida Scott from The Impossible Planet / The Satan Pit feature prominently in Planet Of The Ood. Ida would now be a member of an investigative team looking into conditions on the Ood-Sphere, who would be dismayed to discover that her estranged father is now involved with Ood Operations -- although it would later be revealed that he is secretly acting on behalf of the Ood. In the end, however, it was agreed that Temple should develop entirely new characters for Planet Of The Ood.

When Temple began working on his script, Davies was still devising a new companion who would join the Doctor for the 2008 season. Since both Rose Tyler and Martha Jones had been young women with a romantic attachment to the Doctor, Davies now sought a completely different dynamic. He had been very fond of the interaction between the Doctor and Donna Noble in The Runaway Bride, the 2006 Christmas special, and began thinking in terms of pairing the Doctor with a more mature character who would be less of a willing foil. Indeed, Davies privately wanted to bring Donna back as an ongoing character, but assumed that there was no chance that actress Catherine Tate would be available for nine months' filming. Tate was a high-profile performer in her own right, having already successfully headlined several seasons of her self-titled comedy series, and Davies knew that she constantly in demand.

Instead, Davies decided to craft a new character with Donna-like tendencies. This became Penny Carter, a journalist who would meet the Doctor after discovering that Gary, the boyfriend with whom she's living, is cheating on her. Davies envisaged Penny as having a nagging mother (possibly named Moira) and a grandfather who was a more idealistic stargazer. Davies began seriously developing Penny during February 2007.

In early March, however, he learned from BBC Head of Fiction Jane Tranter that she had recently met with Tate, and raised the possibility of the actress' return to the role of Donna. By this point, Davies was considering bringing back all of the Doctor's past companions for the 2008 finale, and had hoped that Tate might be available for this. To his surprise, Tranter informed him that Tate was actually interested in joining Doctor Who as Donna for the entire season. Davies responded enthusiastically to the proposal, and on March 13th, executive producer Julie Gardner formally offered Tate a contract for all thirteen episodes of the 2008 season. Tate officially accepted on the 19th. Plans to introduce Penny were immediately scrapped, with Donna taking her place. Tate's return to Doctor Who was announced to the press on July 3rd.

Meanwhile, Temple had continued drafting Planet Of The Ood. Its positioning as the season's second episode had now taken on a new importance: since it was a relatively sombre and serious story, Davies felt that it would undermine concerns about Donna being too farcical a character to serve as an ongoing companion. By early August, however, Davies raised concerns that Planet Of The Ood had in fact become too grim to appear so early in the broadcast schedule. It was decided to interchange it in the running order with The Fires Of Pompeii, making it the season's third episode instead. Some of Temple's influences were indeed very dark, such as the 2002 horror film 28 Days Later, which inspired the Ood's feral state. On the other hand, the script also included a nod to the fact that Davies' original conception of the Ood had been inspired by the title aliens from the 1964 serial The Sensorites. It was now suggested that the Ood-Sphere and the Sense-Sphere were actually planets in the same solar system.

The first recording block of the new production schedule consisted solely of the 2007 Christmas special, Voyage Of The Damned. Planet Of The Ood was inserted into Block Two, alongside The Unicorn And The Wasp; these would therefore serve as Tate's reintroduction to filming on Doctor Who, almost one year to the day after she finished work on The Runaway Bride. The director for these two episodes would be Graeme Harper, whose most recent Doctor Who work included 42 and Utopia for the previous season. Since then, Harper had helmed Whatever Happened To Sarah Jane? for the first season of The Sarah Jane Adventures. Producing Block Two would be Susie Liggat, who had also filled the producer's chair for the double-banked Human Nature / The Family Of Blood the year before. This time, Liggat would be filling in for regular producer Phil Collinson in order to give Collinson time to devote to the logistically-complex Voyage Of The Damned and Block Three -- The Fires Of Pompeii -- which featured several days of filming in Italy. As usual, Collinson would instead be credited as an executive producer on the Block Two episodes.

Recording for Planet Of The Ood began on August 21st, with two days at the Upper Boat Studios capturing material in the sales reception area. Shots of an Ood for the advertisement which opens the episode were also performed on the 21st. The surface of the Ood-Sphere was actually Trefil Quarry in Trefil, Gwent, where filming took place on the 23rd. On August 24th and 27th, scenes in the container warehouse were recorded in a hangar at RAF St Athan in Barry. Cast and crew remained in Barry from the 28th to the 31st, when material in the Ood cells and on the grounds of Ood Operations were filmed at Aberthaw Cement Works. The first day of September saw production return to Upper Boat, when various effects shots and the sequences of Bartle's death and of Donna inside the Ood container were taped alongside some of those in Halpen's office. The latter were finished on the 3rd.

The same day, the BBC confirmed that Doctor Who had been renewed for a fifth season -- but revealed that this would not air until the spring of 2010. During the twenty or so months following the conclusion of the 2008 season, a number of specials would air instead, and these would continue to feature David Tennant as the Doctor and Davies as the show's executive producer. This unusual statement about Doctor Who's longterm future was prompted by the Royal Shakespeare Company's announcement at the end of August that Tennant would be appearing in Hamlet and Love's Labour's Lost throughout the latter half of 2008. Since this coincided with Doctor Who's normal production dates, intense speculation followed about the programme's fate. In fact, the gap between seasons had been planned for quite some time: Davies worried that the public would eventually become fatigued with Doctor Who, and felt that after four years on the air, a hiatus of sorts would discourage complacency in the programme's viewers. He also anticipated that he would be leaving Doctor Who around that time, and a year without a full season would facilitate a smoother transition to the next showrunner. A subsidiary benefit of this scheme was Tennant's availability to return to the theatre, something he had been eager to do for some time.

Meanwhile, production on Planet Of The Ood resumed on September 4th, when the Hynix Building in Newport served as the main entrance of Ood Operations. Cast and crew then shifted to the Johnsey Estates in the Mamhilad Park Industrial Estate at Pontypool, where scenes inside Warehouse 15 were recorded. This work continued to the next day, when the Johnsey Estates also provided the corridor outside the Ood cells. An additional shot in Halpen's office, of the Doctor and Donna in restraints, was then filmed at Hensol Castle in Hensol on September 7th. Work on Planet Of The Ood wrapped up two months later, on November 16th. The decision to shift the episode back in the broadcast schedule had necessitated a revision to the TARDIS scene, delaying its recording. This was now completed at Upper Boat, alongside various insert shots.

• Outpost Gallifrey: New Doctor Who Series News Page, edited by Shaun Lyon.
• Doctor Who Magazine Special Edition #20, 19th November 2008, “Episode 3: Planet Of The Ood” 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.