Inspirations: Mummy on the Orient Express

This story had its origins in a seemingly throwaway line in the closing seconds of The Big Bang, the Series 5 finale. The Doctor took a phone call from someone asking him to help out with "an Egyptian goddess loose on the Orient Express - in space".

Writer Jamie Mathieson was already working on his Flatline submission when the title of this episode was handed to him, so impressed was Steven Moffat with the way the other script was developing. Mathieson had contributed to supernatural series Being Human and Dirk Gently.

The title is obviously a play on the Agatha Christie classic Murder on the Orient Express, published in 1933. It was filmed in 1974 with an all-star cast, including Albert Finney as Hercule Poirot. David Suchet gave his (definitive) version of the Belgian detective in a 2010 ITV adaptation, and Kenneth Brannagh has since also featured as Poirot in a 2017 movie adaptation.

Christie also gave us the idea that this space-going Orient Express was visiting the Seven Wonders of the Galaxy, lifted from Death on the Nile. The same idea had previously been used in the 2000AD comic in 1980.

Mathieson was initially concerned that the Mummy was not as versatile a creature as the vampire or werewolf, both of which could hide in plain sight. He worried how something like a Mummy could stay hidden in such an enclosed space as a train - so came up with the idea that it only became visible to its victims just before it killed them.

Initially the Mummy's wrapping were to have had a life of their own, able to sneak under doors etc, and the victims would be mummified themselves.

At one stage it was also envisaged that the Mummy would teleport onto the train in order to kill, residing in a stone tomb the rest of the time, and Clara and Maisie would be transported there for a time instead of being stuck in the baggage car.

(This scene is a prime example of the Bechdel Test in which, in fiction, two women can't hold a conversation without talking about men - the narrative defining them by their relationship to men).

Not quite as popular as vampires or wolfmen, there have been a number of stories and movies about the creatures over the years. The best known cinematic appearances are the Universal and Hammer ones. The first of these - 1932's The Mummy, starring Boris Karloff - isn't actually connected to the subsequent 1940's four film cycle, though they used footage from it for their flashback sequences. Hammer also delivered four Mummy movies, starting with the 1959 film starring Lee and Cushing, and ending with Blood From the Mummy's Tomb in 1971, an adaptation of Bram Stoker's Jewel of the Seven Stars.

The biggest Mummy movies were those starring Brendan Fraser, the first of which was released in 1999. The least said about the execrable Tom Cruise film, the better. It effectively derailed the whole "Universal Dark Universe" franchise before it had really gotten off the ground.

A couple of other early literary works include The Mummy: A Tale of the Twenty Second Century, by Jane Webb (1827), and The Beetle by Richard Marsh (1897).

It was decided that this episode would be double-banked with Mathieson's other story - making it more sense to have the same writer for both - and this meant that Clara had to take more of a back seat here, since Flatline confined Peter Capaldi to the TARDIS and left Jenna Coleman with the lion's share of the plot.

The casting of pop star Foxes came about after she participated in a BBC Showcase event in Liverpool, which Moffat had attended.

Frank Skinner had watched Doctor Who since the very first episode and was a DWM subscriber. He had already featured on a Big Finish audio, and mentioned a desire to appear in the series during several TV interviews.

The first victim, Mrs Pitt, is played by Janet Henfrey - the latest actor to have featured in both the classic series and its revival, having played Miss Hardaker in The Curse of Fenric. Former Doctor Who costume designer June Hudson was also in the running for this part).

Christopher Villiers was another returnee, having played Sir Hugh in The King's Demons.

The Doctor cracks the "Are you my mummy?" joke (The Empty Child / The Doctor Dances) for the second time - having earlier used it to confront gas-masked UNIT soldiers in The Poison Sky.

Among the other Seven Wonders were the Diamond Falls - a reference to Midnight.

Next time: the Doctor's experiencing reduced circumstances so Clara has to play detective to get to the bottom of things, before the situation flattens out completely. Luckily Banksy isn't the only street artist active in Bristol...