Sarah Jane is feeling old, her memory becoming unreliable. When she and her friends confront a platoon of Dark Horde warriors, she forgets vital equipment and endangers them all. Only the intervention of a mysterious adventurer called Ruby White averts disaster. Ruby quickly develops a rapport with Clyde and Rani; she is assisted by an AI called Mr White and has even moved in just down the road. Sarah Jane begins to consider retirement, and she views Ruby as her natural successor. But Ruby is actually a Qetesh: an alien entity which feeds on thrills... and no human leads a more exciting life than Sarah Jane Smith.

During the early stages of planning for the fourth season of The Sarah Jane Adventures, one of the goals was to address what the production team felt was an emerging concern: age. The programme's young characters -- Luke, Clyde and Rani -- were starting to grow appreciably older than the target audience, and there was some apprehension of an adverse effect on the show's appeal. Furthermore, Luke would be playing a diminished role starting in 2010 due to Tommy Knight's decision to focus on his education, leaving The Sarah Jane Adventures short a lead character. As such, a plan was developed to introduce a new regular character in the 2010 finale. This was a “starchild” called Astra, who would be left as a baby on Sarah Jane's doorstep in the closing minutes. The production team then suggested that a Christmas special should be filmed in which it would be revealed that Astra had been placed in Sarah Jane's care by the Doctor. Astra would rapidly age into a teenager -- albeit younger than Clyde and Rani -- and would represent a new take on the wunderkind role which had previously been filled by Luke.

These plans advanced to the point that a script for the Christmas special, called “Miracle On Bannerman Road”, was commissioned from Gareth Roberts and Clayton Hickman. The pair had collaborated on the 2009 Comic Relief skit From Raxacoricofallapatorius With Love..., and Roberts had more recently contributed The Empty Planet to the 2010 season. Inspired by the 1843 Charles Dickens story A Christmas Carol, “Miracle On Bannerman Road” would have seen Sarah Jane assessed by a spectral Guide for her suitability to care for the starchild. Segments would have included a teenaged Sarah Jane stopping a robbery on Christmas Eve, the modern-day Sarah Jane preventing a fire at the Chandras' Christmas party, and a glimpse of a disastrous alien invasion in the near future. It was suggested that the Guide might be played by Tom Baker, who had co-starred with Elisabeth Sladen as the Fourth Doctor.

With no opportunity for a Christmas special, the introduction of the “starchild” was deferred

However, everything changed when CBBC commissioned not just the fourth season of The Sarah Jane Adventures but also the fifth. The revised plan was to make a year and a half's worth of the show -- nine stories split across eighteen episodes -- as part of a single production schedule. This left no opportunity to record a Christmas special, and so the introduction of the new character was deferred to the opening story of the fifth season, Sky, with the title reflecting the new name for the starchild.

Meanwhile, the 2010 finale was intended to be “The Web Of Lies” by script editor Gary Russell. It saw the return of one of Sarah Jane's most memorable Doctor Who nemeses: the Giant Spiders of Metebelis 3, which had originally appeared in 1974's Planet Of The Spiders. It would be revealed that the Giant Spiders had maintained a psychic connection with Sarah Jane down through the years. Their mental control now induced her to steal a Metebelis crystal from Professor Celeste Rivers and the Pharos Institute -- as seen occasionally since 2007's The Lost Boy -- which would be used to evolve the spiders of Earth into more Giant Spiders. However, it would be discovered that Mr Smith's Xylok crystal could be used to counteract the Metebelis crystal and save Sarah Jane.

Around mid-November, Russell concluded that his story was not working out, and so Roberts and Hickman were asked to provide their take on the same basic concept. It was called “Servant Of The Spiders” and again featured Professor Rivers, as well as Toby Silverman, her assistant in 2009's The Eternity Trap. This time, Mr Smith's Xylok crystal was transformed into an approximation of a Metebelis crystal in order to mutate the Earth's spiders; in fact, the Giant Spiders had influenced Sarah Jane's discovery of the Xylok in the first place. However, a humanoid avatar of Mr Smith appeared to Gita Chandra and imbued her with the power to oppose the Giant Spiders. In the end, Sarah Jane's friends inspired her to reject the Giant Spiders' mental control and stop their plans.

As with “The Web Of Lies”, however, the production team was dissatisfied with “Servant Of The Spiders”. Notably, executive producer Russell T Davies found himself increasingly concerned about the unlikelihood of the Bannerman Road gang successfully opposing the Giant Spiders, who had forced the regeneration of the Third Doctor. It became clear that an approach unrelated to Planet Of The Spiders was needed. Consequently, Roberts and Hickman began working on a concept which again had its roots in the maturation of the young characters. Given the departure of Luke for university in the season premiere, The Nightmare Man, and the inevitability that Clyde and Rani would soon grow up and start forging their own paths in the world, the writers wanted to explore how these developments were affecting Sarah Jane. This notion drew on some elements of “Servant Of The Spiders”, in which the Great Spiders' mental control was manifesting in ways that made Sarah Jane seem increasingly dotty and absent-minded.

Ruby was conceived to be comically over the top, but she was toned down to suit the sombre mood

Originally, Roberts and Hickman were asked to include only a small role for Luke. As such, he remained in his dorm room at Oxford University and instructed Mr Smith to send a hologram of the Dark Horde into the dreams of every sleeping person on the planet -- including Haresh Chandra, who fantasised that he was defending Gita from the aliens. Early drafts had Mr White fake a message from Sarah Jane which would be beamed into outer space, daring other races -- such as the Slitheen, the Sontarans and the Sycorax -- to invade the Earth. The writers initially conceived Ruby White to be comically over the top, but they toned down her personality when they came to feel that a sombre mood best suited the story they were telling.

Roberts and Hickman's story was eventually called Goodbye, Sarah Jane Smith, in keeping with Roberts' emotionally-charged trilogy of stories featuring the villainous Trickster: 2007's Whatever Happened To Sarah Jane?, 2008's The Temptation Of Sarah Jane Smith, and 2009's The Wedding Of Sarah Jane Smith. It was directed by Joss Agnew as part of the year's third production block, alongside Lost In Time. Work on Goodbye, Sarah Jane Smith began at the programme's usual recording facilities in Upper Boat. Three days were devoted to the attic set, split across a weekend: May 27th, 28th and 31st, 2010. June 2nd was spent at Clinton Road in Penarth for scenes on Bannerman Road while, on the 3rd, the meteor's impact site was actually Ty Candy Farm at Bridgend. Agnew then concentrated on Lost In Time, except for some inserts taped at Caerphilly Castle in Caerphilly, on June 10th and 11th.

Goodbye, Sarah Jane Smith became Agnew's focus again on June 14th, when scenes in Ruby's basement were filmed at Headlands School in Penarth. This material was completed on the 15th, after which cast and crew returned to Clinton Road for more action on Bannerman Road. Ruby's home really was around the corner from Sarah Jane's house: it was actually a residence on Victoria Road, which intersected with Clinton Road. Sequences there were recorded on June 16th, in addition to more footage on Bannerman Road. Work on the 17th began with the confrontation involving the Dark Horde at a former tinplate works in Rhydyfelin, after which more filming at Upper Boat required the sets for Luke's dorm room and Ruby's prison ship. The serial was completed on June 18th, when scenes in the Chandra residence were taped at Upper Boat.

In editing, Goodbye, Sarah Jane Smith lost a scene on Bannerman Road in which Ruby, Clyde and Rani attempted to trap Travast Polong, the mischievous alien previously glimpsed in The Wedding Of Sarah Jane Smith and 2008's The Mark Of The Berserker. Also dropped from the first episode was material in Ruby's cellar after Sarah Jane requested that Mr Smith perform a med-scan. Davies objected to the early confirmation of the Qetesh's sinister nature, since he felt that it undermined the cliffhanger reveal. For the voice of Mr White, Roberts and Hickman had suggested Ben Miller, who was well known for his comedy partnership with Alexander Armstrong -- the voice of Mr Smith. In the end, this role went to Eddie Marsan, whose many credits included the feature films V For Vendetta, Mission: Impossible III, and the Sherlock Holmes films starring Robert Downey, Jr.

Episode Two of Goodbye, Sarah Jane Smith brought the fourth season of The Sarah Jane Adventures to a close on November 16th. With the first half of the 2011 season already complete, the production team had now turned its attention to the second half, as well as the anticipated sixth season, which was expected to air in 2012. However, as the filming dates neared in the spring of 2011, Sladen revealed that she had been diagnosed with pancreatic cancer in February. The actress had previously suffered from the same illness more than a decade earlier, but this time the prognosis was grim. It was agreed that production of the remaining six episodes of season five would be postponed until 2012, in the hope that Sladen's health would improve in the interim. Sadly, it was not to be: Sladen died on April 19th. Four days later, on April 23rd, the CBBC memorialised the late actress with the broadcast of My Sarah Jane: A Tribute To Elisabeth Sladen following the Doctor Who season premiere, The Impossible Astronaut.

• Doctor Who Magazine Special Edition #28, 13th July 2011, “Episodes 4.11/4.12: Goodbye, Sarah Jane Smith” 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.