A strange force affects the TARDIS, stranding the Doctor on modern-day Earth while Amy is trapped in the rapidly deteriorating time machine. The Doctor traces the mysterious influence to a seemingly ordinary home in Colchester, where the mysterious occupant of the top-floor apartment lures people up the stairs, never to be seen again. Fortunately, the downstairs tenant, Craig Owens, is advertising for a roommate. The Doctor answers Craig's ad -- and proceeds to turn the young man's life upside-down.

Although Gareth Roberts' first televised Doctor Who episode had been Season Twenty-Nine's The Shakespeare Code, this was not his first idea for a TV script. Earlier, Roberts had contemplated a story in which Rose Tyler and her mum, Jackie, become trapped in the TARDIS, forcing the Doctor to live with Mickey Smith. Roberts ultimately decided to use this idea for a comic strip in Doctor Who Magazine, and The Lodger was published in 2006. Doctor Who scriptwriter Steven Moffat recommended the tale to then-showrunner Russell T Davies, but by that point in time, Rose and Mickey were being written out of the series, so there was no possibility of adapting it for television.

Moffat did not forget The Lodger, however, and when he agreed to succeed Davies as executive producer of Doctor Who in 2007, he invited Roberts to write for his first season, suggesting The Lodger as a starting point. However, by the time Moffat and Roberts began serious discussions about the episode in September 2008, Moffat had other ideas he wanted Roberts to pursue. Roberts then began work on this alternative script; it was developed through to July 2009, only to be dropped at that point.

In its place, Roberts suggested to Moffat that he revisit The Lodger. This 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 slate. Furthermore, since it would involve the Doctor's companion (now Amy Pond) trapped in the TARDIS for most of the story, its filming could overlap that of another episode in case the shooting schedule needed to be compressed. Moffat gave Roberts the green light to transform The Lodger into a full television script.

In the comic strip version, the villains had been the alien Bandrigans, who were really a sidebar to the Doctor/Mickey shenanigans. For the TV version, Roberts knew he would need a more substantial threat. Because the narrative dealt with someone manipulating time and space, Roberts thought of the eponymous villain of Season Eighteen's Meglos. Moffat was amused by the idea of bringing back the little-loved Zolfa-Thuran shapeshifter -- the script would even see the Doctor 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”.

Unfortunately, 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 Meglos. Furthermore, Simon Nye's Amy's Choice, which would air earlier in Season Thirty-One, also featured extraterrestrials masquerading as pensioners. Happily, however, it had also been realised that there was more money available for Roberts' script than had originally been anticipated. With this in mind, Moffat suggested that Meglos be replaced with a grander climax involving a malfunctioning time machine and its metamorphosing Avatar.

Other changes to Roberts' script were less significant. The writer had initially included more scenes drawn directly from the comic strip version of The Lodger, such as the Doctor beating his flatmate Craig Owens (replacing Mickey Smith) in a first-person-shooter videogame by making peace with their intended targets, and the Doctor annoying the participants in a pub quiz by getting every answer right. One key scene that did survive was the Doctor joining Craig's football team. This very much played to Matt Smith's talents, since the actor had seriously planned a career as a professional footballer until a back injury ended this dream when he was 16 years old. There was originally a fourth victim of the Avatar, a middle-aged man named Martin who would leave behind a holiday magazine which would later serve as an additional clue that the Avatar is targetting people who want to get away. Craig's apartment was located on Aickman Road; this was an homage to Robert Aickman, author of numerous supernatural “strange stories”.

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. Production began with the Aickman Road exteriors, filmed on Westville Road in Cardiff on May 3rd and 4th. The next day, Matt Smith had the chance to display his football prowess while taping 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 the location where the Doctor became separated from Amy and the TARDIS. The week ended at Lanelay Hall in Pontyclun, Llantrisant, which posed as Craig's workplace on May 6th. Around this time, the title of the episode reverted to The Lodger.

The rest of Morshead's shoot was confined to Upper Boat Studios, beginning with scenes in the rogue time capsule on May 8th. Material in Craig's flat and the hallway outside was then filmed from the 9th to the 12th, and from the 15th to the 20th; the TARDIS set was also in use on the 17th and 20th. This marked the end of filming for Season Thirty-One. Meanwhile, Roberts was still advocating for the episode to be called “Something At The Top Of The Stairs”, but there were concerns that this was too lengthy. In April, a compromise was attempted with “Don't Go Up The Stairs”, but in May, the title was finalised as The Lodger.

• Doctor Who News.
• Doctor Who Magazine Special Edition #27, 16th March 2011, “The Lodger” by Andrew Pixley, Panini Publishing Ltd.