Already struggling to keep her life in the TARDIS separate from her relationship with Danny Pink, Clara is astonished when the Doctor arrives at Coal Hill School. He is tracking a lethal alien war machine called the Skovox Blitzer, and is posing as the school caretaker to facilitate his search. But the Doctor's efforts to snare the robot in a time trap are complicated by the involvement of school troublemaker Courtney Woods. To make matters worse, a frosty rapport develops between the Time Lord and an unsuspecting Danny -- which comes to a head when Danny inadvertently foils the Doctor's plan to deal with the Blitzer.

The structure of Doctor Who's thirty-fourth season was dictated, in part, by executive producer Steven Moffat's plan to develop the character of companion Clara Oswald. A love interest, fellow teacher Danny Pink, was introduced in the year's second episode, Into The Dalek. Moffat then wanted to spend the first half of the season exploring the tension that resulted from Clara's efforts to keep Danny unaware of her adventures with the Doctor. This would come to a head at the season's midway point -- episode six -- when the Doctor and Danny would finally collide, and Clara's secrets would be revealed.

To write this pivotal story, Moffat turned to Doctor Who veteran Gareth Roberts. In addition to regular work on the spin-off series The Sarah Jane Adventures, in recent years Roberts had also written two scripts for Matt Smith's Eleventh Doctor: Season Thirty-One's well-received The Lodger and its sequel, the subsequent year's Closing Time. Both had placed the Doctor in a mundane modern setting, and Moffat particularly enjoyed the manner in which The Lodger had forced the Doctor to try to adapt to everyday life. He suggested a similar approach for the new narrative, with the Doctor taking a job at Coal Hill Secondary School, where both Clara and Danny were teachers. Moffat and Roberts would ultimately share the writing credit for the resulting adventure.

The head teacher was initially Miss Coburn, named after the writer of the original Doctor Who serial, 100,000 BC

Roberts began writing the script, eventually called The Caretaker, during the summer of 2013. The Blitzer was initially identified as a relic of a war between the Skovox and the Olverites. The Doctor's plan was to teleport it back to its planet of origin -- instead of the distant future -- and Danny's interference simply gave it a chance to escape, rather than propelling it three days forward in time. The Blitzer's refuge was an abandoned house, but it became a derelict industrial site to provide more space for the war machine to move around. The head teacher was initially Miss Coburn; she was named after Anthony Coburn, the writer of the original Doctor Who serial, 1963's 100,000 BC, which had been partly set at Coal Hill School. Miss Coburn was ultimately replaced with Mr Armitage in order to align with Into The Dalek.

Upon learning of the premise of The Caretaker, producer Nikki Wilson suggested that the Doctor should develop a rapport with one of the students. Roberts initially devised Courtney Woods as a junior version of Amy Pond, the Eleventh Doctor's popular companion -- thereby reinforcing the story's echoing of that era which most obviously manifested in the lookalike schoolteacher, Adrian. However, this approach was soon reconsidered, and Roberts instead developed Courtney as a defiant troublemaker. The character proved popular with the production team, and it was agreed that Courtney would be inserted into both the season premiere, Deep Breath, and Into The Dalek.

The Caretaker was paired with episode three, Robot Of Sherwood, as Block Three of the Season Thirty-Four production schedule, directed by Paul Murphy. Since the nature of the other adventure meant that it would benefit from being recorded a little further into the spring, most of The Caretaker was made first. As such, the initial work on the episode took place on March 24th, with an empty building on Bute Street in Cardiff serving as the Blitzer's lair. The war machine itself made its debut on this day, operated from within by diminutive actor Jimmy Vee. The Blitzer's design was inspired by Babyface, the cannibalised toy made from a doll's head and an erector-set-constructed spider body in the 1995 animated film Toy Story.

The rest of the week was largely confined to Roath Lock Studios in Cardiff. March 25th was spent on the desert planet interlude; plans to record green screen shots of the Blitzer were scuppered by a fire alarm. The 26th and 27th then focussed on scenes which required the TARDIS set; part of the latter day also saw a change of venue to the nearby Doctor Who Experience -- a permanent exhibition on Cardiff Bay -- for the material in the spaceship corridor. Work on March 28th began with sequences in Clara's flat. Cast and crew then moved to the standing pub set used for the medical drama Casualty, where a suspiciously-tanned Clara met Danny for a date. Finally, the black cab was situated on the backlot of the Welsh-language soap opera Pobol y Cwm. Production then stood down for a four-day weekend, spanning Saturday to Tuesday.

Almost all of the remaining scenes for The Caretaker were those set at Coal Hill, for which no fewer than four actual schools were employed. April 2nd and 3rd brought Murphy's team to Gladstone Primary School in Cardiff, which offered space suitable for the caretaker's storeroom. Recording on the 4th took place at the former St Illtyd's Boys' College in Cardiff. Scenes taped there included those in the staff room, Clara's classroom, and various corridors, plus the Blitzer tracking the Doctor in an adjacent alleyway. The location on April 5th was Holton Primary School in Barry, for sequences outside the storeroom and on the playground. Sunday the 6th and Monday the 7th were days off, after which Tonyrefail School in Tonyrefail hosted all of the week's work on The Caretaker. Recording on April 8th took place in the gymnasium. The school hall and various corridors then became the chief concern from the 9th to the 11th, alongside the school entrance on the first two days and the courtyard on the last day; Murphy also shot a number of inserts.

The team then concentrated on Robot Of Sherwood, not returning to The Caretaker until April 28th. The day's filming at Roath Lock included material in the TARDIS console room, over-the-shoulder shots looking through the police box doors, and green screen effects for Courtney gazing at the Olveron Cluster, plus the deferred footage of the Blitzer. On June 11th, more pick-ups and green screen shots were completed at Roath Lock. However, the major feature of the day was a new closing scene for The Caretaker which saw Matthew, the deceased Community Support Officer, meet the unsettling Seb in the Nethersphere. This material was actually recorded in the costume preparation area of Roath Lock, which offered a distinctive round window. Finally, the glimpse of Michelle Gomez as Missy was taped at Enfys Television Studios in Cardiff on June 18th.

During the first few weeks of Season Thirty-Four, Doctor Who had been routinely assigned a 7.30pm timeslot. This would change with the broadcast of The Caretaker on September 27th, as the BBC's reality juggernaut Strictly Come Dancing returned for its twelfth season. With the celebrity competition effectively taking its place in the schedule, Doctor Who was pushed further into the evening, rather than being brought forward to a more typical early timeslot. Each episode was now slated to begin at 8.30pm, the latest start time that Doctor Who had ever occupied on a regular basis. Strictly Come Dancing would serve as its new lead-in, with Casualty positioned afterwards. Although there was a significant outcry -- with concern notably being expressed that children would no longer be able to stay up late enough to watch Doctor Who -- there would be little change to this schedule for the remainder of the year.

• The Doctor Who Companion -- The Twelfth Doctor: Volume Two, October 2019, “The Caretaker” by Andrew Pixley, Panini UK Ltd.
• Doctor Who: The Complete History #78, 2017, “Story 247: The Caretaker”, edited by Mark Wright, Hachette Partworks Ltd.