The Face of Boe summons the Doctor and Rose to a hospital on New Earth in the far future. The facility is run by the cat-like Sisters of Plenitude, and the Doctor is astonished to find that their medical technology is centuries ahead of its time. Suspicious of how the Sisters have achieved such advancements, he discovers secret holding cells full of sick and dying humans, being experimented upon against their will. Meanwhile Cassandra, the last human, has survived her apparent death on Platform One and is lurking in the bowels of the hospital. There she uses a psychograft to displace Rose's mind and take control of her body.

With work well under way on his first season of Doctor Who, executive producer Russell T Davies started to turn his thoughts towards a prospective second run. His initial idea for the Season Twenty-Eight premiere was a full-scale alien invasion of Earth which would lean heavily on familiar characters to help viewers adapt to the newly-introduced Tenth Doctor. On February 2nd, 2005, however, the BBC commissioned not only a 2006 season of Doctor Who but also a special episode for Christmas 2005. Davies decided to bring forward his alien assault narrative, which became The Christmas Invasion; a new storyline would be required for Season Twenty-Eight's debut installment.

One of the early successes of Season Twenty-Seven was the second episode, The End Of The World. Considerable word of mouth was excited by its far-future setting and panoply of alien creatures, with the audience in general -- and Davies himself -- becoming notably fond of the villainous Cassandra, voiced by Zoë Wanamaker. Davies still felt that the 2006 premiere should include familiar elements from the previous year, and he began to consider the possibility of paying an annual visit to the Year Five Billion setting of The End Of The World. As such, he started to develop an idea he dubbed “Body Swap”. Since the digitally-rendered Cassandra had been a challenging and expensive element of The End Of The World, the character would spend most of the new narrative inhabiting the bodies of others -- particularly Rose Tyler. This would help satisfy Billie Piper's desire for more light-hearted material, after Season Twenty-Seven had regularly put her character through an emotional wringer.

Doctor Who's renewal for a third season prompted Russell T Davies to postpone the Face of Boe's revelation by a year

In addition to Cassandra, Davies decided to revisit another character from The End Of The World: the monolithic Face of Boe. The mysterious being had also made a cameo appearance in Season Twenty-Seven's The Long Game, which was set in the year 200,000. It was thus implied that the creature's lifespan was immense, and Davies had decided that the Face of Boe would harbour a secret with very personal implications for the Doctor: that he, the putative last of the Time Lords, was not alone. Originally, this secret was to be divulged at the end of “Body Swap”. On June 15th, however, it was confirmed that Doctor Who's renewal had been extended to include a third season. This prompted Davies to postpone the Face of Boe's revelation by a year.

“Body Swap” was initially set on a planet named Coffra, but this had changed by July, at which point the adventure was known as New Earth. The Sisters of Patience became the Sisters of Plenitude, and the medical facility was called the Hospital of Evergreen Days at one stage. Cassandra's servant was envisaged as a dwarf named Zaggit but, as the character's importance grew during the scripting process, he developed into Chip. The climax of the story changed significantly from Davies' original conception. At first, the Doctor would have been forced to let the Intensive Care patients die, but Davies came up with a more optimistic solution when Steven Moffat -- who had written 2005's The Empty Child / The Doctor Dances -- observed that Davies had a penchant for creating interesting characters and then killing them off.

New Earth formed part of Season Twenty-Eight's first production block, directed by James Hawes alongside The Christmas Invasion and episode three, School Reunion. An early concern was Wanamaker's availability, since she would be required to make an on-screen appearance in the story's closing moments, in addition to providing Cassandra's dialogue. Wanamaker had thoroughly enjoyed her involvement with The End Of The World, but she was already committed to Cards On The Table, an episode of Poirot, during the planned recording dates for New Earth. Davies contemplated the possibility of reimagining the villain of the piece to be Cassandra's heretofore unrevealed sister, who could be played by a different actress. Fortunately, however, arrangements were made for Wanamaker to film the party scene on August 1st -- more than a month ahead of the majority of the episode -- at the Ba Orient restaurant in Cardiff. The same day, the departure of the TARDIS from London was recorded at Canal Park. Hawes was otherwise focussing on The Christmas Invasion at this point, for which Piper was wearing hair extensions to hide the fact that she had a shorter haircut for the new season. As a result, she was given an up-do for the Ba Orient sequence, and donned a cap at Canal Park.

On August 22nd, HTV Wales Studios in Cardiff played host to special effects work and shots of the Intensive Care patients. It wasn't until early September that recording for New Earth finally picked up in earnest, starting on September 5th when material in the hospital foyer was taped at Cardiff's Millennium Centre. By this time, most of The Christmas Invasion and School Reunion had been completed, and Block One as a whole had fallen badly behind schedule. As a result, several scenes were dropped from Hawes' plans, many of which involved the Duke of Manhattan and Frau Clovis. Originally, they first appeared in the hospital foyer during the Doctor's arrival; as scripted, he immediately earned the disdain of the Sisters of Plenitude when he saved the Duke's life. Later, Clovis mutinied when the Duke refused to help defend the hospital against the Intensive Care patients.

With Hawes' original schedule in disarray, the only work carried out on New Earth over September 6th and 7th took place at the BBC Model Unit Stage in Acton, London and involved smoke effects. Principal photography resumed on the 9th and 10th, when the disused Ely Paper Mill in Cardiff played host to scenes in the Intensive Care Unit. Cast and crew then spent a week at Unit Q2, the main Doctor Who studio facility in Newport. September 12th to 16th focussed on scenes in the hospital wards and shafts alongside various inserts, with part of the last day also dedicated to the standing TARDIS set. Work on the 13th was interrupted when Piper's boyfriend, Amadu Sowe, inadvertently damaged the Face of Boe prop, necessitating hasty repairs. Location filming resumed on September 19th at Tredegar House in Newport, where material in Cassandra's lair was recorded. Unfortunately, Piper was badly ill, forcing Hawes to curtail his plans for the day and defer the scenes he had planned to record on the 20th. Piper was well enough to return to work at Tredegar House on the 21st, with shooting there concluding on the 22nd. The latter day also saw additional inserts captured at Unit Q2.

The shoot at Worm's Head in Rhossili was hampered by driving wind and rain

With Block One now running beyond its intended end date, the sequences outside the TARDIS on New Earth were filmed on September 26th, at Worm's Head in Rhossili on the Gower Peninsula. Unfortunately, the shoot was hampered by driving wind and rain, and insufficient daylight forced the abandonment of the last scene to be recorded. Intended to bridge the final hospital sequence and the material at Cassandra's party, it was replaced by a voiceover from the Doctor. The uncooperative weather was not the only misfortune to befall the day's work: it was belatedly discovered that a camera had malfunctioned during the shoot, resulting in the loss of various close-ups. Two more days at Unit Q2 were needed on October 7th and 8th. The first day was primarily concerned with the Doctor and Rose being disinfected in the hospital lifts, while the second day saw their rapid descent down the lift shaft recorded alongside various pick-ups. Then, on November 3rd, an additional insert of the Doctor emerging from the TARDIS at Cassandra's party was taped at Unit Q2.

Although New Earth had been designed to serve as the season premiere, Davies reconsidered its position in the schedule more than once. Before production began, he had suggested that it might swap places with Moffat's The Girl In The Fireplace which, at that stage, was intended to be the second story in the broadcast order. Closer to transmission, there was discussion about running Davies' own Tooth And Claw first and then New Earth second; the latter's fraught production had provoked some concern that it didn't represent Doctor Who at its best, and might discourage an audience which was still becoming accustomed to David Tennant's Doctor. Indeed, the opening scene involving the Doctor and Rose had been written and recorded such that it could easily be appended to the start of a different episode, if need be. In the end, however, it was agreed that New Earth was naturally suited for the pole position, while Jane Tranter, the BBC's Controller of Drama Commissioning, felt that its relatively light-hearted narrative was a more appropriate season premiere than the atmospheric Tooth And Claw.

Not long before the transmission of New Earth, producer Phil Collinson requested changes to some of the computer-generated effects involving the hospital exterior. Previously, the facility had been depicted as being isolated, but Collinson thought that the absence of other buildings looked unnatural. Additional structures and new architectural detail were hastily added to the images in response to his criticisms.

The TARDISode for New Earth became available on March 31st, 2006

Part of the promotional campaign for Doctor Who's 2006 season was the development of one-minute prologues, to be released in advance of each episode. Written by Gareth Roberts -- who had also scripted the Attack Of The Graske interactive game which had appeared on the BBC's digital service at Christmas 2005 -- the teasers could be downloaded from the BBC's Doctor Who website or accessed via a mobile phone. After names such as “Whosode”, “Epi-mobe” and “Who Alert” were considered, the videos were dubbed “Vortext”; at a late stage, however, they were rechristened TARDISodes. The forty-six-second TARDISode for New Earth took the form of an advertisement for the hospital, and featured Anna Hope reprising her role as Novice Hame. It was recorded on January 31st, 2006 at Enfys Television Studios in Cardiff. The TARDISode became available on March 31st.

Two weeks later, New Earth repeated the pattern established by the 2005 season and debuted on Easter Saturday, April 15th. As had been the case for much of the previous year, it was scheduled between Strictly Dance Fever and The National Lottery: Jet Set, although its 7.15pm timeslot was a quarter of an hour later than Season Twenty-Seven's. Strictly Dance Fever was brought forward to an earlier time to accommodate the start of Doctor Who's new run.

• Doctor Who Magazine Special Edition #14, 9th November 2006, “Episode 1: New Earth” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #51, 2015, “Story 168: New Earth”, edited by John Ainsworth, Hachette Partworks Ltd.
• Doctor Who: The Inside Story by Gary Russell (2006), BBC Books.