The mystery of who’s in the vault beneath the university was revealed in the sixth episode of Doctor Who Season 10. And while a lot of fans guessed who (or what) it was from the very beginning, that doesn’t mean the Doctor’s (Peter Capaldi) life is going to get any simpler. Then again, when is this show ever simple?

This post contains weird, timey-wimey spoilers for Doctor Who Season 10, Episode 6, “Extremis.”

Yep, it was Michelle Gomez’s Missy. “Extremis” jumps back and forth between two storylines, with the Doctor acting as an “executioner” for Missy in one and the still-blinded Doctor, Bill (Pearl Mackie), and Nardole (Matt Lucas) working with the Catholic church and a bunch of world-conquering aliens in the other.

The episode finally sets up some sort of larger plot for the season, which has been sorely missing from the first five episodes. It turns out there’s a race of red-robed, Dementors-from-Harry-Potter-looking aliens bent on taking over Earth. But we’re getting ahead of ourselves. Let’s take a step back and figure out how we got to this point.

Michelle Gomez's Missy returns for 'Doctor Who' Season 10 and is revealed as the person inside the Doctor's vault.

Bill is on a date with a girl named Penny when the TARDIS lands in Bill’s bedroom, and the Pope — yes, that Pope — runs out and starts yelling in Italian. Penny leaves and Bill, annoyed, follows the Doctor and Nardole to the Vatican to help the Pope and his cardinals with a problem. It turns out there’s this ancient text known only as the “Veritas” that causes people to kill themselves after they read it.

The Doctor, still blind after his romp through the vacuum of space and determined to read the Veritas after the Pope begged him for help, sends Bill and Nardole off on their own so he can restore his sight. Using a weird box thing, the Doctor shocks himself to temporarily regain sight, although, he explains, doing so will sacrifice something in the future, possibly from one of his future regenerations. Maybe, he posits, he won’t be able to regenerate at all.

Bill (Pearl Mackie) and Nardole (Matt Lucas)

Meanwhile, Nardole and Bill find a set of portals in a round, white room. They pop in and out of the United States Pentagon before finding their way to CERN (the European Organization for Nuclear Research). There, Bill and Nardole discover that all the scientists plan to kill themselves because they’ve also read the Veritas. One of the scientists, baffled to find that neither Bill nor Nardole has read the Veritas, conducts an experiment, asking them to say a random number. Everyone in the room is able to say the same number at the same time, and Bill and Nardole are terrified by what that could mean.

After the scientists have died in a dynamite-induced explosion, Bill and Nardole return to the white portal room where Nardole makes a horrifying discovery: Everything around them is a simulation.

Nardole, reaching past the edge of the simulation, disappears into the ether, and Bill finds her way back to the Doctor. He’s sitting in a simulation of the Oval Office, and he explains to her that an alien race (the Dementor-looking things) are using different simulations of Earth to test-run invasion plans. The Bill, Doctor, and Nardole we’ve been following throughout this episode aren’t really them. They’re simulations under the impression of being the real thing.

The Doctor (Peter Capaldi) with a Monk

Confronting one of the aliens, the Doctor is able to get a message to his real self using his sonic sunglasses just in time before the alien dissolves that simulation, ready to start anew.

The shot jumps to the real Doctor, still blind, receiving a message from his simulated self while sitting in front of the vault. He’s ready to go to war to protect Earth, but he’s going to need some help. Luckily, it turns out Missy is in the vault.

In the other timeline we’ve been following in the episode, the Doctor doesn’t execute Missy so much as shock her into unconsciousness for a bit. He’s meant to place her inside a vault (this is 1,000 years in the past from the present timeline) and watch over her body for 1,000 years. So, that’s what he does. And thank the Time Lords the 1,000 years seems to be coming to an end. The Doctor is going to need Missy’s help for this mission.


Doctor Who Season 10 airs on BBC and BBC America on Saturdays at 9 p.m. Eastern.

Photos via BBC