Inspirations: Oxygen

In 2005, former CEO of Nestlé Peter Brabeck-Letmathe tried to argue that water was not a human right. It was simply a commodity like anything you might buy in a shop, and had a market value.

By 2013 he had backtracked in his view, following the understandable outcry. 

It's this sort of commercialisation of what most would agree to be a basic human necessity which forms the backdrop to this episode.

We are in deep space, and the essential element here is oxygen. A mining rig on an otherwise lifeless asteroid is owned by a faceless corporation on Earth, and its crew have to pay for their air supply.

There's no safety net. If your stock runs out, you suffocate and die.

The story began life as a request from Steven Moffat to writer Jamie Mathieson for an adventure set in outer space. The showrunner wanted it to highlight just how hostile and deadly space could be. He had been inspired by the recent movie Gravity and the 1995 film Apollo 13.

Mathieson's original idea was of a spaceship graveyard. A group of survivors were being forced to jump from wreck to wreck in search of oxygen and other supplies, hunted all the time by savage crystalline monsters.

They were controlled by a queen who dwelt on a nearby asteroid. She mimicked distress signals to ensnare passing ships. An additional complication was that the survivor group consisted of people from opposing factions in a war. There was also an element of The Thing, in that the monsters could mentally manipulate people, so paranoia was rife amongst the survivors.

The story would have ended with an ethical debate about whether or not they should kill the queen.

It was then decided to ditch the monsters, other than the queen, and simply have space itself the threat, but with the additional danger of zombies - animated human cadavers. These would have some sort of intelligence, however. It was the queen which controlled them. 

The spaceship graveyard was still the setting, and the people encountered by the Doctor and Bill were now simply shipwrecked scavengers.

This time, the episode ended with the Doctor forming a psychic link with the queen to stop it from killing.

Two of the characters were named after family friends of the writer - Darren and his son Ivan, who was a fan of the show. The former became Dahh-Ren, who was originally going to have a multi-eyed spider-like face. Budget restraints reduced this to him simply having blue skin.

As much as Moffat liked the story, he asked Mathieson to pare it down to essentials. He proposed that the zombies be manipulated by their spacesuits. He was worried that they might resemble too closely the skeletons in spacesuits from his own Silence in the Library / Forest of the Dead.

The more zombified look of the cadavers - exposed to the vacuum of space - was retained.

It was Moffat who then suggested that the crew of a mining vessel be forced to purchase their oxygen from the corporation which employed them. This could be withheld if the operation was unprofitable.

An added threat was that the smartsuits could electrocute their owner or anyone they touch.

The suits quite literally become the menace.

"Suits" is slang for business executives and bosses - i.e. the men in suits who run things.

Together Moffat and Mathieson decided on bringing back GUS from the writer's previous story Mummy on the Orient Express, whose origins had been left vague. This would stand for Ganymede Systems.

Mathieson then drew on his own experience of working long hours for bad wages for large corporations.

In the end, the references to GUS would be dropped.

The mining vessel was named Chasm Forge, after the Valley Forge from the 1972 ecological sci-fi movie Silent Running.

Mathieson proposed that the Doctor should be blinded for the second half of the story, after sacrificing his sight to save Bill. He later suggested that the Doctor remain blind at the end of the story - expecting this to be rejected. Moffat decided to incorporate this into the next two scripts.

Nardole's role in Series 10 had only developed late in the day, and he was originally going to be brought into the story after the Doctor and Bill set off without realising he was on the TARDIS.

He didn't feature in the earlier drafts.

At one point the Doctor lies to Nardole about one of the fluid links. He had first used these as an excuse to explore in The Daleks, and they were a feature of other stories such as The Wheel in Space and The Mind Robber.

The Doctor had previously been seen to do a space walk, in a helmet with oxygen but no face visor, in Four to Doomsday, where he claimed to be able to survive this environment for up to 6 minutes.

Next time: monk-y business in the Vatican...