Having chaperoned an overnight class trip, Clara and Danny awaken in the morning to discover that a forest has grown up all across the world. Amongst the trees infesting London, the Doctor meets Maebh, one of their pupils. Troubled ever since the disappearance of her sister a year earlier, Maebh now seems to have developed a strange connection to the mysterious events. When she goes missing, the Doctor and Clara set off into the woods to find her. In the process, they discover that a deadly solar flare is hurtling towards the Earth -- but are the trees another agent of the planet's destruction, or of its salvation?

As Doctor Who executive producer Steven Moffat was developing the programme's thirty-fourth season, he was put in contact with writer Frank Cottrell-Boyce by his predecessor, Russell T Davies. Early in their careers, Cottrell-Boyce and Davies had worked together on the supernatural soap opera Springhill, after which Cottrell-Boyce had written several feature films and become an award-winning children's author. Nonetheless, he harboured an admiration for Doctor Who which dated back to the days of Jon Pertwee's Third Doctor, and he had finally decided to approach the production team about contributing to the series. Eager to bring aboard a writer of Cottrell-Boyce's pedigree, the production team responded in early 2014 to discuss potential story ideas.

Thinking in terms of the Third Doctor's adventures in contemporary London during his exile to Earth by the Time Lords, Cottrell-Boyce aimed to devise a narrative which would similarly bring peril close to home for the audience. This prompted the notion of a contemporary London which had become mysteriously overgrown. Cottrell-Boyce thought that presenting the natural world as the apparent threat would place the Doctor in an unusually powerless position. The premise would also echo many beloved fairy tales, which were often set in deep, dark woods which embodied humanity's primal fear of the unknown. Originally, the Doctor believed that the strange events were specifically targeted at him, but Moffat discouraged this approach.

Maebh's surname was a reference to the Forest of Arden in Warwickshire

Cottrell-Boyce's untitled first draft was completed in mid-April. At this stage, the goal of the worldwide phone call was to use the noise of the ringing phones to create a resonance pattern in the clouds, which would initiate a protective rainfall. Although it would be ambiguous in the final episode, the voices which spoke through Maebh were intended to be called the Here. Maebh's surname, Arden, was a reference to the Forest of Arden in Warwickshire; now much diminished from its once vast extent, it was also the setting of William Shakespeare's 1599 comedy As You Like It. Ruby's name was inspired by her identification of the red ring in the tree trunk. Samson was initially called Noah.

By the start of June, the adventure was called In The Forest Of The Night; the title was derived from William Blake's poem The Tyger, published in the 1794 collection Songs Of Experience. It was positioned as the tenth episode of the season, immediately prior to the two-part finale, Dark Water / Death In Heaven. As such, the Doctor's reunion with the Master -- now calling herself Missy and played by Michelle Gomez -- was to be presaged by a message from the Here to the Doctor, delivered by Maebh: “You are not alone.” This was the same omen which the Face of Boe communicated to the Tenth Doctor in 2007's Gridlock, laying the groundwork for the introduction of a new Master portrayed by John Simm later that year.

Since In The Forest Of The Night would benefit from being recorded once the Welsh greenery was in full flourish, it was scheduled on its own as Block Seven, at the end of the Season Thirty-Four production calendar. The director would be Sheree Folkson, making her only Doctor Who episode. Whereas the season's first six blocks had alternated between producers Nikki Wilson and Peter Bennett, Block Seven would be overseen by Paul Frift, who was new to the series. He had been working in film and television since the early Eighties, initially as an assistant director. He rose to become an associate producer and a line producer starting in the early Nineties, and then worked regularly as a producer from 2007 on shows like Primeval, Crooked House and The Escape Artist. Amongst the predominantly school-aged cast was Harley Bird, playing Ruby. She was then in the midst of a ten-year stint as the voice of the popular animated character Peppa Pig, but this would mark a rare on-screen appearance for the actress.

Folkson undertook one day of filming at Roath Lock Studios in Cardiff during the pre-production period. This was July 11th, and included both Missy's cameo appearance and the Minister's appeal. The first day of the regular shoot, July 22nd, was also based at Roath Lock, this time with cameras rolling on the standing TARDIS set. The major location for In The Forest Of The Night was the Caerwent Training Area in Caerwent. The woodland around the disused Ministry of Defense establishment was dressed as the overgrown London, with filming taking place from July 23rd to 25th and then, after the weekend, from the 28th to the 31st. On the other hand, the heart of the forest where the Here communicated via Maebh was actually Fforest Fawr in Taff's Well, where cast and crew spent August 1st.

The production again stood down for the weekend, before resuming on August 4th at the National Museum of Wales in Cardiff. Cottrell-Boyce had originally scripted the venue to be the Science Museum in London and then the city's Natural History Museum, before it became the fictitious London Zoological Museum. Folkson was unable to complete all of the shots she had planned for the National Museum, resulting in the omission of a scene where Maebh's mum, Siobhan, arrived to find the building abandoned. Filming on August 5th started at the former St Illtyd's Boys' College in Cardiff, which once again posed as Coal Hill School. Folkson's team then returned to Roath Lock for material on Clara's balcony, plus additional footage in the TARDIS. Studio recording on the 6th began on a mock-up of the museum entrance; it was thought that the unfilmed sequence with Siobhan might be remounted, but this did not occur. Later in the day, Folkson completed the remaining TARDIS footage and the effects shot of the Doctor and Clara watching the solar flare, as well as a number of inserts.

Material involving the wild animals was recorded at the premises of the Amazing Animals firm in Heythrop, Oxfordshire

On August 7th, Peter Capaldi and Jenna Coleman embarked on a world tour to publicise Season Thirty-Four; running through to the 18th, it would take them to seven cities and every continent except Africa and Antarctica. Nonetheless, Folkson still had some outstanding material to record which did not require the Doctor or Clara. On the 7th, sequences at the Arden home were filmed at a residence on Partridge Road in Cardiff, alongside pick-up shots of Maebh in the woods. Folkson's team returned to the Caerwent Training Area on August 8th, when work included the appearance of Breakfast presenter Jenny Hill as herself. The news reports from Paris, France and Accra, Ghana were also taped there. This left only the material involving the wild animals, which was arranged with the involvement of the Amazing Animals firm and recorded at their premises on the grounds of the Heythrop Zoological Gardens in Heythrop, Oxfordshire. The tiger was the focus on August 13th, followed by the wolves on the 14th.

One of the scenes dropped from In The Forest Of The Night during editing involved the Doctor describing the childhood vision he experienced when he gazed into the Untempered Schism on Gallifrey, as first discussed in 2007's The Sound Of Drums. He told Clara that he watched as aeons passed by in seconds, and a mighty forest rose and fell, much as the trees had suddenly sprung up on Earth overnight. His companion wondered if Gallifrey -- now established as having been lost in another dimension following the events of 2013's The Day Of The Doctor -- could be involved, foreshadowing the Doctor's attempt to find his home planet in Death In Heaven.

In The Forest Of The Night aired on October 18th. Doctor Who's timeslot was moved five minutes earlier than the previous week's Flatline -- to 8.20pm -- as a dwindling number of contestants meant a shorter runtime for its lead-in, reality competition Strictly Come Dancing.

• The Doctor Who Companion -- The Twelfth Doctor: Volume Three, February 2020, “In The Forest Of The Night” by Andrew Pixley, Panini UK Ltd.
• Doctor Who: The Complete History #79, 2018, “Story 251: In The Forest Of The Night”, edited by John Ainsworth, Hachette Partworks Ltd.