Doctor Who: “Mummy on the Orient Express”
(Episode 8.08)

Per the title, Doctor Who again tackles Agatha Christie, placing The Doctor in the role of Hercule Poirot. It’s framed as a bittersweet adventure since Clara (looking quite amazing in her flapper attire) makes it clear to The Doctor from the get-go that this will be their last “hurrah.” She’ll be leaving the TARDIS for good once they return to Earth. This makes for an even more intense emotional ride as, in the course of the episode, her fears about The Doctor’s worst tendencies are assuaged then confirmed, then subsequently subverted.
In any case, this seemingly relaxing adventure becomes (predictably) yet another life-and-death scenario when The Doctor and Clara discover that someone or something has been killing train passengers. Yes indeed, even as an advanced space train, The Orient Express can’t escape its destiny as a place where people seem to find themselves bereft of life.
That being said, this set up is less of a “whodunit”—we know from the beginning that a mysterious mummy figure is killing the victims—and more of a “whatisit.” The mummy creature is unique in that it appears only to a specific person—and only them, no one else can see it—then proceeds to kill them in exactly 66 seconds. Here again, we have another high-concept monster that’s become synonymous with the Moffat era (though, it should be noted, this particular episode was penned by Jamie Mathieson).
As The Doctor tries to figure out the situation by interrogating the train’s crew (including a highly intelligent, if slightly malevolent-seeming engineer named Perkins), Clara finds herself helping out a traumatized passenger named Maisie, whose grandmother was the mummy’s first victim.
As with “Kill the Moon,” this entry makes an abrupt left turn halfway through the runtime. The Doctor eventually deduces that, far from being a luxurious means of travel, The Orient Express is some kind of experiment designed by an unseen being named GUS to determine the exact nature of the mummy and how to stop it. Whatever the creature is, it appears to have something to do with an old, burnt scroll that hangs at the end of one train car. Also, it seems to target its victims based on their health, whether it be physical ailments (diseases, organ transplants) or psychological ones (trauma, stress, etc.).
With the situation out of his hands, the only thing The Doctor can do is have each of the mummy’s victims relay details about the monster in the 66 seconds before they are killed. Were this David Tennant’s Doctor, one could hear him whispering, “I am so sorry…” to the passengers as they look to him, desperate for help in the moments before death. However, Peter Capaldi’s Doctor, as pointed out by one of the victims, has little time for such beside manner. Thus, when The Doctor orders Maisie to the main train car under the guise that he knows how to save her, one could legitimately believe that The Doctor would let her die, simply to get more information.