BBC AmericaNobody keeps Missy in a vault, except for the Doctor, apparently.
Throughout the first few episodes of this season of Doctor Who, we've all been wondering what the hell the Doctor (Peter Capaldi) was protecting in that big vault. We knew that he had made some sort of oath to stay on Earth unless it was an emergency (a rule which he has not been following so far this season) so that he could make sure the vault was secure. He had taken a job as a university professor and stashed the vault in his office and had Nardole (Matt Lucas) bothering him about it all the time, but we didn't know what exactly he was protecting...until now.
As many had started to suspect based on the fact that we knew she was returning, we learned tonight that Missy (Michelle Gomez) is in that vault, and the Doctor had made his vow to the executioners he had saved Missy from. He has to keep her out of trouble for 1000 years, just because he's the only other Time Lord around.
Tonight's episode also revealed one hell of a problem that might take a few episodes to deal with: some very scary aliens have been running simulations of the world to see how easy it will be to take it over, and the Doctor, Bill, and Nardole have all been in one of those simulations. The truth could only be found in a book in the Vatican that was causing anyone who read it to kill themselves, but instead of killing himself, the Doctor (who's still blind, by the way) emailed the documents to another version of himself, who knocked on the vault and asked Missy for help.
As for what Missy can actually do to help, Michelle Gomez could not say, exactly.
"Because she's a Time Lord as well, she has certain tools at her disposal that she can put into play and try and divert the catastrophe that may or may not be about to hit," Gomez told E! News somewhat vaguely over the phone. "It's up to her how much she uses her forces for good or evil."
Gomez also couldn't really tell us much about Missy's plan for getting out of that vault.
"She has an ejector seat in her underpants so she just blows herself out," she joked. "There may be a vortex manipulator involved. There may be a key involved. I can't get into that, but all I can say is that for dramatic effect, there will probably be more use for having Missy out of that vault than keeping her in it."
What she could say, however, is that we are in for one hell of a second half of a season, especially given that this is the end for both Capaldi and showrunner Steven Moffat, who's been at the helm since 2009.
"If Steven was ambitious with his imagining before, just try and guess what he's up to coming to the end of his time there," Gomez told us. "Put it this way: everybody had to work really hard to make his ambition happen and I think we've done it... Steven Moffat's certainly not going out quietly."
One thing we can look forward to is Missy meeting up with a former incarnation of The Master, played by John Simm.
Moffat told Radio Times that he always thought "it'd be fun to have a story where two versions of The Master meet," and that Simm had always wanted to come back after we last saw him in 2010, so that's exactly what's happening later this season.
"That's where the acting challenge comes in, because it's basically a Master with two heads, which was really silly and fun at times," Gomez told us. "We're both sort of acting as one. That's where the challenge came in, and I think we pulled it off."
And if you need other things to get you excited for what's to come, Gomez has a whole list.
"The bangs and crashes are really good and the bits that blow up and the other people that fall down and those awful moments with that terrible thing in the corner, and oh my god, what is that coming through the air vents," she says. "And my stuff too is quite good. And also Matt Lucas makes me laugh."
As much as this season is a goodbye to Moffat and a goodbye to Capaldi, who's also leaving later this year, it might also be a goodbye to Gomez, who said that while "you never know" with Missy, it feels like the end of an era for her.
However, if new showrunner Chris Chibnall were to ask Gomez to return, she says she wouldn't say no.
"I think that would be churlish," she says. "But I think at the moment they've got other things to focus on than whether Michelle's coming back as the Master or not. I will probably pop up at some point, but I think they've got a lot more to focus on at the moment."
If it is the end for her, Gomez says she'll have a lot to miss.
"That I was in it," she said when we asked what she'd miss the most. "That's really a big part of it for me, that I was invited into that world and I got to be a 50 year-old action figure basically out there. There was not a cardigan in sight. It was a really wonderful opportunity for me to be as powerful and unpredictable as I got to be on a daily basis. It was a real gift."
For now, however, Missy's not going anywhere.
"Let's just say Missy's along for the finale, so they're definitely getting their money's worth out of me," she says. "I'll put it that way."
Doctor Who airs Saturdays at 9 p.m. on BBC America.