No sooner has the Doctor stepped out of the TARDIS into modern-day England than it dematerialises again, trapping Amy inside. A strange force is preventing the time machine from landing, and the Doctor traces it to a seemingly ordinary house in Colchester. The downstairs resident, Craig Owens, is searching for a roommate, so the Doctor moves in. Soon, he's inadvertently involved himself in every aspect of Craig's life -- including his unspoken love for his best friend, Sophie. Meanwhile, a toxic stain is forming on Craig's ceiling... and the mysterious tenant on the top floor is luring people up the stairs, never to be seen again.

Although Gareth Roberts' first televised Doctor Who episode was Season Twenty-Nine's The Shakespeare Code, it was not his first idea for the programme. Earlier, he had contemplated a story in which companion Rose Tyler and her mum, Jackie, became trapped in the future with the TARDIS. Stuck in the present day, the Doctor would be forced to live with Rose's ex-boyfriend, Mickey Smith, until his scheme to plant instructions for Rose in old nursery rhymes helped her pilot the TARDIS back to him. Roberts ultimately decided to use the flat-sharing core of this narrative for a comic strip in Doctor Who Magazine, and The Lodger was published in 2006. Doctor Who scriptwriter Steven Moffat subsequently suggested to executive producer Russell T Davies that it might be worthy of developing for television. By that point in time, however, Rose and Mickey were being written out of the series, and the notion was not pursued.

In 2007, Moffat agreed to be Davies' successor on Doctor Who. He had not forgotten The Lodger, and he suggested that Roberts should consider how it could be adapted for the screen. However, by the time Moffat and Roberts began serious discussions about the episode in September 2008, Moffat had identified other ideas which he wanted Roberts to pursue. In late 2008, Roberts finished work on Planet Of The Dead, one of the final specials for David Tennant's Tenth Doctor, which he and Davies were co-writing. He then turned his attention to an adventure called “Death To The Doctor”, only to see it abandoned in July 2009.

It was not clear that there was room in Season 31 for The Lodger

At this stage, it was not clear that there was room in Season Thirty-One for an alternative script from Roberts, since only the latter recording blocks remained fluid. All the same, Roberts reminded Moffat about The Lodger. The straightforward narrative was now particularly appealing because it could be written as a budget-conscious episode -- something that was always crucial late in the Doctor Who production schedule, when funds often started to run low.

The minimal role for the Doctor's companion -- now Amy Pond -- was also a potential advantage. In recent years, each season had required two episodes to be in production simultaneously in order to accommodate the filming of a Christmas special alongside the thirteen-part regular season. This wasn't necessary for Season Thirty-One, because the 2009 Christmas special had been made by Davies' production team, while its as-yet-unconfirmed 2010 counterpart would be recorded alongside Season Thirty-Two. Nonetheless, Moffat was mindful that any substantial delays during the nine-month shoot might necessitate the compression of the production schedule, and double-banking was an easy way to accomplish this. In that case, the Doctor-centric The Lodger could be paired with an episode focussing on Amy, in a manner similar to Season Thirty's Midnight and Turn Left.

With these considerations in mind, Moffat gave Roberts the green light to develop his script. In the comic strip version of The Lodger, the villains had been the alien Bandrigans, who were effectively little more than a sidebar to the Doctor/Mickey shenanigans. For the television version, Roberts knew he needed a more substantial threat. Because the narrative dealt with someone manipulating time, Roberts thought of the eponymous villain of 1980's Meglos, who had tried to trap the Fourth Doctor in a time loop. Moffat was amused by the idea of bringing back the little-loved Zolfa-Thuran shapeshifter -- the Doctor would even admit to having forgotten their previous encounter -- and because the alien would be disguised as a little old lady, the episode became facetiously known as “Mrs Meglos”.

In December, a spot opened up for Roberts' script when budgetary considerations forced the postponement of episode eleven -- Neil Gaiman's The Doctor's Wife -- to Season Thirty-Two. However, two developments in early 2010 forced Roberts and Moffat to rethink Meglos' return. First, the final Tenth Doctor story, The End Of Time, introduced the alien Vinvocci, whose cactus-like appearance was similar to that of Meglos. Furthermore, Simon Nye's Amy's Choice, which would air earlier in Season Thirty-One, also featured extraterrestrials masquerading as senior citizens. On the other hand, it was realised that more money was available for Roberts' script than had been anticipated. As a result, Moffat suggested that Meglos should be replaced with the grander notion of a malfunctioning time machine and its metamorphosing Avatar.

The Doctor's involvement with Craig's football team played to Matt Smith's talents

Other changes to Roberts' script were less significant, including the omission of several elements drawn directly from the comic strip version of The Lodger. A scene in which the Doctor annoyed the participants in a pub quiz by getting every answer right was dropped in order to reduce the number of required locations. Another sequence would have seen the Doctor beating his flatmate, Craig Owens, in a first-person-shooter video game by making peace with their intended targets. Having been conceived to take Mickey's place, Craig initially retained a lot of the mistrust of the Doctor which had been part of Mickey's character when the comic was published. This trait was dropped when Roberts realised that it no longer had a justification. One key scene that did survive was the Doctor's involvement with Craig's football team. It very much played to Matt Smith's talents, since the actor had been heading towards a career as a professional footballer until he suffered a serious back injury when he was sixteen years old.

As production neared, it was determined that there was no need to double-bank The Lodger with another episode. This allowed Roberts to add more material for Karen Gillan as Amy. There was originally a fourth victim of the Avatar: a middle-aged man named Martin. He was to leave behind a holiday magazine, which would later serve as an additional clue that the Avatar was targeting people who wanted to get away. Another character present in early drafts was a woman who regularly appeared outside Craig's house, commenting on the action. At one stage, the climax saw Craig rescue Sophie while the Doctor shut down the rogue time machine; it was Moffat who suggested combining these two elements. The Doctor was also to indicate that the time ship had crashed into Craig's building, killing its crew. The device which the Doctor constructed out of everyday objects was reminiscent of the time flow analogue which the Third Doctor built in 1972's The Time Monster. The flat's address on Aickman Road was an homage to Robert Aickman, the author of numerous supernatural “strange stories” found in collections such as 1976's Cold Hand In Mine.

By the end of February, Roberts' script was known as “Something At The Top Of The Stairs”. It formed part of the seventh and final recording block for Season Thirty-One alongside Amy's Choice, under the direction of Catherine Morshead. The design of the rogue time machine drew upon ideas which concept artist Matthew Savage had developed the previous spring. They were originally intended for the new TARDIS console room, which was introduced at the start of the season in The Eleventh Hour.

Production on “Something At The Top Of The Stairs” began on March 3rd and 4th, with Westville Road in Cardiff posing as Aickman Road. Smith had the chance to display his football prowess on the 5th, during the match which pitted the Doctor and his Kings Head team against the Rising Sun. The venue for these sequences was Cardiff's Victoria Park, which was also where the Doctor became separated from Amy and the TARDIS. The week ended at Lanelay Hall in Pontyclun, which served as Craig's workplace on March 6th. Around this time, the title of the episode reverted to The Lodger.

Following a day off on Sunday the 7th, the rest of Morshead's shoot was confined to Doctor Who's usual studio facilities in Upper Boat. Work began with scenes in the rogue time capsule on March 8th. The main set for The Lodger was Craig's flat and the hallway outside. It was in use from March 9th to 12th, and again after the weekend from the 15th to the 19th. Other recording during the last week included Gillan's solo TARDIS scenes on the 17th and 18th, and a number of pick-up shots on the 19th. Finally, production on Season Thirty-One came to an end on March 20th, which saw the Doctor and Amy reunited on the TARDIS set, and an insert taped for the appearance of the crack in time behind Craig's refrigerator. Two days earlier, at the premiere of The Eleventh Hour in Cardiff, executive producer Piers Wenger had confirmed the commissioning of Doctor Who's thirty-second season, alongside a Christmas special for 2010.

During post-production, Roberts was still advocating for the episode to be called “Something At The Top Of The Stairs”, but there were concerns about the title's length. In April, a compromise was attempted with “Don't Go Up The Stairs” but, in May, the title reverted permanently to The Lodger. The episode aired on June 12th, at the slightly later time of 6.45pm to accommodate a World Cup match between Argentina and Nigeria that afternoon. On this occasion, Doctor Who was preceded by a special edition of Total Wipeout, which had been its regular lead-in earlier in the season.

• Doctor Who Magazine Special Edition #27, 16th March 2011, “The Lodger” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #65, 2018, “Story 211: The Lodger”, edited by John Ainsworth, Hachette Partworks Ltd.