One night, Mr Smith detects an untraceable alien signal. Nothing seems amiss... until the next morning, when Rani and Clyde awaken to find that Sarah Jane, their parents, and indeed everybody on Bannerman Road have all vanished. Even Mr Smith does not respond to their commands. Heading into town, they find that London is deserted, with only a frightened boy named Gavin left behind. But suddenly, strange sounds fill the air, alien symbols appear on every television screen, and robots roam the streets. Can Clyde and Rani solve the mystery of the empty planet?

Gareth Roberts was a frequent contributor to The Sarah Jane Adventures, having most recently written The Wedding Of Sarah Jane Smith for the programme's third season. For season four, he was initially asked to provide an emotionally-challenging story for Sarah Jane -- in the vein of 2008's The Temptation Of Sarah Jane Smith -- as the year's third serial. However, when it became clear that this notion wasn't working out, Roberts was asked to start over with a different concept. It would now be scheduled as the fourth adventure of the 2010 season, since Matt Smith's availability to play the Eleventh Doctor had shifted Death Of The Doctor to the third spot.

Roberts began work on an adventure featuring Professor Celeste Rivers and the Pharos Institute, an occasional presence in the show ever since The Lost Boy in 2007. Here, Rivers alerted Sarah Jane to an organisation called Alpha Solutions which had poached most of the Pharos staff -- including Toby Silverman, her assistant in 2009's The Eternity Trap. Going undercover, Sarah Jane discovered that Alpha was experimenting on a captive alien to synthesise an enzyme which bestowed super-strength. However, the production team ultimately felt that the tenor of Roberts' storyline was wrong for The Sarah Jane Adventures, and the writer agreed to develop something else.

The idea for The Empty Planet had been devised by Russell T Davies in 2007 for Doctor Who

The new idea assigned to Roberts was one which executive producer Russell T Davies had initially devised in December 2007 for Doctor Who. During the press launch for the second season of its other spin-off series, Torchwood, Davies had found himself walking the eerily empty halls of a London hotel, and he began to think about a story in which the father of a family suddenly found himself all alone -- until he ran into the Doctor. Davies opted not to use this notion for the 2008 Doctor Who Christmas special, which instead became The Next Doctor. However, it was then given to Phil Ford to develop as a possible collaboration for broadcast at Christmas 2009. Ford's storyline was called “A Midwinter's Tale”, but Davies had misgivings about the concept, and he and Ford would ultimately write The Waters Of Mars in its place.

For Roberts' version of the storyline, which was ultimately called The Empty Planet, the deserted hotel setting was abandoned, since the action would focus on Clyde and Rani as the only humans left on Earth. The lack of emphasis on Sarah Jane was intentional, in order to provide Elisabeth Sladen with her usual mid-season break. Considerable thought was given to the explanation for why Clyde and Rani had not vanished along with the rest of humanity, before finally settling on their being confined to Earth by Captain Tybo in 2009's Prisoner Of The Judoon.

In early drafts, Gavin was not an alien prince but a shapechanging villain, who had fled to Earth and taken the form of the first person he met. The robots were pursuing him because he had stolen a power source from their peaceful homeworld; Gavin planned to plug this device into Mr Smith and use it to take over the planet. At the end of the story, Rani called the real Gavin to make sure that he was safe. The suddenness of humanity's disappearance was originally made more explicit, taking place after Rani had woken up for the morning, with the sounds of her parents getting ready for the day abruptly cut off. Another change was the removal of the notion that the robots communicated only through musical sounds.

The Empty Planet was recorded alongside Death Of The Doctor as the year's second production block. On April 26th, 2010, director Ashley Way taped material in the attic and the Chandra residence at the programme's regular studio home in Upper Boat. In order to most effectively portray the abandoned London streets, it was agreed that some filming would have to take place on Sundays, when the cast and crew normally stood down. The first of these was May 9th, which was spent on Skinner Street in Newport. Newport remained the venue for the next three days, with locations in use on the 10th including the Coffee Shop (for the cafe where Clyde and Rani tried to figure out what was happening), Bon Marché (the clothing store where Clyde hid from the yellow robot), and the Park Square Car Park (atop which Clyde and Rani looked out on the deserted London, achieved via green screen). Way's team returned to the Coffee Shop on the 11th and 12th, with work on the latter day continuing with more street scenes recorded in and around Market Street and Upper Dock Street.

Filming on May 13th began on the grounds of a private home in St Nicholas, where Gavin accepted his destiny. The aftermath in which the Earth was restored to normal was then taped at Alexandra Park in Penarth. The second Sunday of the shoot was May 16th, which saw action play out in and around Commercial Street and Kear Court, back in Newport. Bannerman Road scenes were completed at Clinton Road in Penarth on the 18th. May 19th and 20th focussed on sequences at Gavin's home, which was actually an apartment on Channel View Road in Cardiff. Part of the latter day was also spent at Maes y Felin Farm in Dyffryn, for the flashback to Gavin's homeworld of Kravasta. Finally, more material in Rani's house was taped at Upper Boat on the 21st.

Jocelyn Jee Esien had been hired to return as Carla Langer for The Curse Of Clyde Langer

In editing, it was realised that Episode One of The Empty Planet was running significantly under-length, and so several new scenes were written to extend the narrative. Most were set in the Chandra home, and included a replacement version of Rani's return at the end of the serial; it was scheduled to be filmed at Clinton Road on April 27th, but wound up being cancelled due to heavy rain. Jocelyn Jee Esien had been hired to return as Carla Langer for the second story of the 2011 season, The Curse Of Clyde Langer, having originated the role in 2008's The Mark Of The Berserker. This provided the opportunity to add a new sequence to The Empty Planet in which Carla and her son discussed Clyde's artistic acumen. All of the new material was filmed at Upper Boat on July 11th.

Roberts had intended that The Empty Planet would boast no incidental music whatsoever, starting with the scene of Rani waking up to a deserted house through to the restoration of the Earth's populace. However, Way was concerned that this would be to the serial's detriment, and a very sparse score was instead composed by Sam Watts. Also unusual was the decision to omit a pre-credits sequence at the start of Episode One.

A further oddity for The Empty Planet was that its second installment actually debuted in high definition before its first. This was because, to that point, there was only a single high definition BBC channel: BBC HD. It broadcast programmes which were transmitted in standard definition throughout the BBC family, and was on the air for only about nine hours per day. As a result, the high-definition broadcast of some shows was substantially delayed. For example, the first few episodes of the 2010 season of The Sarah Jane Adventures were airing one per week on BBC HD, rather than two per week as on CBBC and BBC One, meaning that they were falling farther and farther behind their standard-definition counterparts. On November 3rd, however, the BBC launched BBC One HD, which would air high-definition versions of all BBC One programmes in a simulcast with the standard-definition channel. BBC HD would remain as a home for high-definition versions of other BBC programmes, until it was replaced with BBC Two HD in March 2013. The Empty Planet Episode Two was the first installment of The Sarah Jane Adventures to benefit from this new arrangement; Episode One would not receive its high-definition transmission until BBC HD caught up, on December 12th.

• Doctor Who Magazine Special Edition #28, 13th July 2011, “Episodes 4.7/4.8: The Empty Planet” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who Magazine Special Edition #32, Autumn 2012, “The Stories That Never Were...” by Andrew Pixley, Panini UK Ltd.