Tonight's episode "Mummy on the Orient Express" begins with an elderly woman being attacked on a train by a mummy that only she can see, resulting in her dying of a heart attack. Later, the Doctor takes Clara to that same train, the Orient Express. However, this is actually a space train! They've come here for Clara's last adventure with him; she decided to end their relationship following last week's episode.
Once aboard, they meet Maisie, the granddaughter of the woman who was just killed, and they find out about the alleged mummy. They also meet Quell, the ship's captain who's trying to keep a lid on things, along with Perkins, the chief engineer. The Doctor begins contemplating the mummy situation and seeks the knowledge of Moorhouse, an expert on myths who's also traveling on the Orient Express. They discuss the legend of the Foretold, a creature seen only by its victims who kills in 66 seconds. It is said to be immortal and cannot be harmed by conventional weapons. The Doctor believes this is the culprit behind the woman's death. As they are discussing this, one of the cooks aboard the train is killed by the Foretold.
Meanwhile, Clara and Maisie break into a storage compartment to see the woman's body. Maisie explains this is out of guilt because she often wished her grandmother dead (Granny wasn't such a nice person, apparently). However, they get locked in and are stuck.
The Doctor and Moorhouse investigate the recent deaths and discover the electricity faltered during each. The Doctor goes to find Clara but can't get through the locked door. Just then, Captain Quell arrives to arrest him on suspicion of being the murderer (the Doctor had been pretending to be a mystery shopper up to this point). But another death occurs, and Quell releases him. The Foretold then kills Moorhouse, and the Doctor tells the crew to bring him the background data on the victims. As it turns out, each of them was sick in either body or mind, causing the Doctor to conclude the mummy is targeting the weakest people first. The Doctor also realizes the passengers are experts in different fields, specifically chosen, and he demands to know who's pulling the strings.
At that moment, the train's upper-class facade is revealed to be a series of holograms (along with most of the passengers), and a lab takes its place. A mysterious man known only as Gus uses the PA system to announce he's brought them together to capture the Foretold so he can reverse-engineer its abilities. And to show he means business, he decompresses the kitchen, sucking the cooks into space.
The Foretold then kills Quell, and the Doctor discovers Maisie is the next victim. He urges Clara to bring her to him so he can watch the mummy attack her, instructing her to lie if necessary. Clara does lie, telling Maisie the Doctor can save her. They go to him, and the Foretold attacks. However, the Doctor manages to steal her negative emotions (the reason the mummy was targeting her), thus becoming the new target. He confronts the Foretold and determines the bandaged menace is actually a soldier who was equipped with a teleporter and cursed with immortality by having to suck the energy from the living. Knowing the soldier just wants his war to end, the Doctor surrenders. The Foretold disintegrates, and the Doctor acquires his teleporter. Unfortunately, Gus doesn't want witnesses, and shuts off oxygen to the car they're in. The Doctor manages to activate the teleporter and get them off the train.
He takes everyone to a nearby planet, and he and Clara have a talk. Her faith in him is restored following his rescue of Maisie, but he explains it's not that simple. Sometimes you have to make bad choices, he says. If Maisie had died, he would have simply moved onto the next victim and kept fighting the Foretold. Nevertheless, Clara decides to keep traveling with him.
Tonight's episode was another strong one. I especially liked the exploration of the Doctor's morality. He's not a clear-cut black-and-white figure. He has his flaws, but he keeps doing his best to do the right thing, and we are again reminded he needs an emotional anchor like Clara to keep him grounded. Also, as a fan of the anime Galaxy Express 999, I dig the space train concept. Finally, I'm intrigued by the mystery of Gus, and I hope he shows up again down the road.