Remember that shock fans had when Missy told Eleven that she used to be the Master?  That’s nothing compared to the two shocks fans got in this week’s episode. It started as a dry run over whether Missy can be truly reformed, and ends with a shock no one will ever forget.

SPOILERS BELOW

While some fans were aware of the return of John Simm as the previous Master (the one who was Prime Minister for a while),  they may have been stunned about how he came back. It’s also been known that Pearl Mackie, fantastic as Bill, would be with us for only this season, although there was hope she’d stay somehow. After what happened, her fate may have been sealed. First things first, though…

The episode starts with the Doctor landing in a very cold place, and we see him start to regenerate. He yells, “NOOOO!”, as the process begins.

Cut to the past, where Missy comes out of the TARDIS calling herself “Doctor Who” and identifies Bill and Nardole as her “expendables” at one point. It’s a funny “audition” for Missy, who thinks the idea of being like the Doctor rather amusing.

They’re in a space station that’s supposed to be picking up colonists. It’s very close to a black hole, in the process of moving away from it.

Suddenly, a blue guy named Jorj comes in and asks which one of them is human. The Doctor comes in and tells Jorj (Oliver Lansley) to calm down. Jorj doesn’t and accidentally blasts a hole in Bill. Seeing that hole in the middle of her chest, and her face in horror, is a pretty disturbing shot.

After a flashback where the Doctor and Bill discuss reforming Missy by letting her do what he does, and Bill asking the Doctor to make sure she doesn’t get killed, some strange-looking men take Bill’s body and promises to “repair” her. They are attached to IV’s and covered in cloth. Hmmmm.

Bill’s heart is repaired after which she meets other cloth-covered people with IV’s. Then Bill meets a weird (even for Doctor Who) guy named Razor and a nurse who tells Bill she’s now a janitor. Bill learns her heart will stop working if she tries to escape.

Bill learns that time passes differently in parts of the ship because it’s close to the black hole. Razor says they’re at the bottom of the ship, and time passes quicker than the top where the Doctor is. The descendants who live at the bottom are suffering from deteriorating conditions. They have to “convert” their bodies so they can get to the top of the ship. If anyone suspects Bill is going to be part of this conversion, it’s worse than that.

All the while, she sees the Doctor telling her “Wait for me.” He sent that into her subconscious. It’s the only piece of hope she has.

It isn’t long before Bill runs into more “converted” people, including a couple that might look familiar to those who saw “The Tenth Planet”. Suddenly one of the surgeons sees Bill and tells her it’s her turn to be converted. Razor is near her, apologizing (sort of) for tricking her.

While this is going on, the Doctor, Missy and Nardole manage to pull a fast one on Jorj, and take the elevator below. The Doctor and Nardole find an operating room, while Missy looks through the computer.

Then Razor sees Missy, and seems to be really pleased to see her. She threatens him, of course, and finds the space station isn’t from Earth but its twin planet Mondas. That should be a big hint for older fans. Razor is stunned that Missy hasn’t recognized him. Well, he was pretty good at disguises, especially in the 1980’s. Once he mentions he used to be Prime Minster, he pulls off his mask…. and he’s the Master (John Simm). Apparently he’s worried about his “future”, but after one look at him, Missy embraces her previous self.

This will upset the Doctor, since he wanted to reform Missy because she’s the only person closest to him. Still, it was inevitable she would return to her dark ways.

Meanwhile, the Doctor and Nardole are confronted by a Mondasian Cyberman who seems to know the Doctor. They ask where is Bill.

They don’t like its answer:  “I am Bill Potts”.

That last image, Bill’s eye with a tear, will not be forgotten. Neither will her last words:  “I waited for you.”

This has got to be one of the biggest tragedies on the show since Adric’s death in Earthshock. This will put a cloud over the Doctor for some time.

Overall, the episode promised an interesting story about whether an evil Time Lady can change her spots. Instead, it gave us a big shock that seemed to be resolved, along with clues that maybe things are about to get worse. It saved its most shocking twists in the final four minutes. Showrunner and script writer Steven Moffat is giving us quite a finale for himself and Peter Capaldi. Sadly, it may also suggest Pearl Mackie will be gone, too. Some had been hoping she’d help out the next Doctor, as Jenna Coleman did when Capaldi started.

For the record, Michelle Gomez would have filled the Doctor’s shoes perfectly.

Next week, the Doctor has to join with both Masters to battle the Cybermen. Will he fall anyway?