The Doctor takes Bill to an Earth colony in the far future, only to find an empty city. The advance team -- which should be preparing for the colonists' arrival -- is missing. The only inhabitants are robots with heads that display emoji, which serve as the interface for the Vardies, a nanobot swarm from which the city is built. The time travellers discover that the advance team was murdered by the Vardies, which are targeting anybody who expresses a negative emotion. The Doctor realises that the city is a giant deathtrap which must be destroyed -- but it falls to Bill to discover the real reason for the Vardy mutiny.

After completing In The Forest Of The Night for Doctor Who's thirty-fourth season, Frank Cottrell-Boyce was approached by executive producer Brian Minchin about a second contribution to the series. With the writer busy on other projects, he was eventually allocated the second episode of Season Thirty-Six, which would chronicle new companion Bill Potts' first journey into the future. It was agreed that the setting would be a virtually empty colony world, since this would permit the emerging relationship between the Doctor and Bill to remain a principal focus of the story. Keen to draw upon genuine scientific notions in his work, Cottrell-Boyce had developed relationships with various academics including Tim O'Brien, an astrophysicist at the University of Manchester. He suggested that much of the initial work of establishing a human colony on another planet would probably be performed by robots; indeed, this had been the idea behind the Mechonoids of 1965's The Chase.

Eager to portray a future which would appear bright and optimistic -- at least on the surface -- Cottrell-Boyce created an environment which would largely be regulated by an advanced form of artificial intelligence. A key element of the narrative would then become the thorny ethical issue of the artificial intelligence's autonomy after achieving a form of self-awareness. The notion of a nanobot swarm was inspired by another of Cottrell-Boyce's contacts, Andrew Vardy, a computer scientist at Memorial University of Newfoundland in St John's, Newfoundland and Labrador, at Canada's uttermost east. His specialty was swarm robotics, and especially robots which operated based on biologically-inspired principles; Cottrell-Boyce duly decided to call his nanobots Vardies.

By May 2016, Frank Cottrell-Boyce's script was entitled “The News From Nowhere”

By May 2016, Cottrell-Boyce's script was entitled “The News From Nowhere”. The title referred to News From Nowhere (or An Epoch Of Rest), an 1890 novel by William Morris which was set in an agrarian utopia. The planet to which humanity had come was ultimately called Gliese 581 D, but Cottrell-Boyce had previously dubbed it Erehwon, which instead became the name of the colony ship. It was derived from Samuel Butler's satirical 1872 novel Erewhon, or Over The Range which was set in a newly-discovered country called Erewhon -- an anagram of “Nowhere”. At this stage, the Vardies were described as having an appearance like tiny hedgehogs. In the opening scene on the colony world, Kezzia's sister was called Sam rather than Goodthing, and their mother's death was the first loss of life on the planet. It was Kezzia and Sam's resultant grief that triggered the Vardies' initial attack. The next wave of colonists arrived on a second spaceship, and the Doctor and Bill left after encouraging them to flee the city.

By mid-June, the adventure was called Smile. This change helped to emphasise the involvement of the Emojibots, of which Cottrell-Boyce was particularly proud. He thought that audiences would be able to understand the colony world's utopian ideal by association with the freedom and versatility which emoji had brought to modern-day communication. Emoji had emerged around the turn of the twenty-first century as a more sophisticated refinement of text-based emoticons, which were a hallmark of the early Internet during the Eighties and Nineties.

Directed by Lawrence Gough, Smile was paired with episode one, The Pilot, as Season Thirty-Six's first production block. Amongst the cast was Mina Anwar, playing the ill-fated Goodthing. She had previously enjoyed a regular role as Gita Chandra in the last four seasons of the spin-off series The Sarah Jane Adventures. Minchin had produced the final two years of the show, during which he had learned that Anwar was keen to appear in Doctor Who as well.

Gough spent the early weeks of Block One making The Pilot, so the first recording for Smile didn't take place until July 8th. This was the material in the greenhouse, which was actually located at Flemingston Court Farm in Flemingston. With the season premiere largely complete, Gough finally focussed on Cottrell-Boyce's script from July 12th. Work on this day took place at Roath Lock Studios in Cardiff, and involved TARDIS sequences -- including Matt Lucas' only contribution to the episode as Nardole -- as well as greenhouse inserts. For the interior of the spaceship, cast and crew travelled to Uskmouth Power Station in Newport, where the cameras were rolling from July 13th to 15th.

After the weekend, recording at Uskmouth Power Station continued on July 18th and 19th; various pick-up shots were also captured on the latter day. Scenes in the wheat field -- part of Gileston Farm in Gileston -- were taped on the 20th. July 21st and 22nd were spent at Roath Lock, primarily for sequences in the great hall. The latter day also saw Gough capture footage in some of the city's corridors, a shot of Bill watching the TARDIS monitor, and a number of inserts.

Although some parts of the Vardy city were realised as sets, it was felt that the requisite scale could only be achieved on location. With the Doctor Who team having recently made several successful excursions to film on Spain's Canary Islands, Minchin suggested that another Spanish venue would be appropriate for Smile. This was the Ciutat de les Arts i les Ciències -- the City of Arts and Sciences -- in Valencia, near the country's east coast. Situated in a dry riverbed, construction of the Ciutat had begun in 1996. It was opened in 1998, with building continuing until 2009.

Cast and crew left the United Kingdom on Sunday the 24th for a shoot spanning July 25th to 28th. A key venue utilised on all four days was the Hemisfèric, the first structure completed in the Ciutat, which housed a planetarium and a cinema. It was the scene of the attack in the pre-credits sequence, the place where the Doctor and Bill first encountered the Emojibots, and the site of the entrance to the spaceship. Other work on the 25th included the Doctor and Bill's arrival in the city at the Museu de les Ciències, which had been designed to resemble a whale's skeleton. The Doctor and Bill ate their meal at the Palau de les Arts on the 26th; the opera hall's exterior was where the time travellers effected their initial escape from the city. On the 27th, Bill's discovery of the skeletons took place along the landscaped walking path of the Umbracle.

With filming for Smile nearly finished, Gough's team flew home on the 29th. The major remaining sequence was the throw-forward to episode three, Thin Ice, was which taped during its production at Roath Lock on September 1st. Finally, an insert of Bill touching the TARDIS sign was recorded in the studio on September 15th. Smile aired on April 22nd, 2017 in the same 7.20pm timeslot as The Pilot the week before. On this occasion, however, the FA Cup semi-final between Chelsea and Tottenham Hotspur took the place of Pointless Celebrities as Doctor Who's lead-in.

• Doctor Who: The Complete History #86, 2018, “Story 266: Smile”, edited by Mark Wright, Hachette Partworks Ltd.