There’s one villain in Doctor Who whose mysterious survival against impossible odds never needs explanation. Sometimes we get one — say, “those rejuvenating flames, rather than cremating me, actually rejuvenated me! Go figure!” or “I took over someone else’s body. I can do that now” — but more often than not, he just shows up, grinning like a fiend.

We’ll come back to him. But if somehow you don’t already know who I’m talking about, and why, maybe go watch “Dark Water” first.

I’m surprised to actually have guessed three out of four of the big reveals in this episode. I’m probably in good company, but the good news here is that they were no less satisfying for having been expected. I suspected that Danny would be the next soldier to be inducted into the Nethersphere, and that this would be what drew the Doctor and Clara there (reveal 1). As lukewarm as I am on Clara these days, Jenna Coleman once again knocked her performance out of the park, particularly in the kitchen scene, lost in numb grief on the way to determination to get the Doctor to help her find Danny. The scene where she destroys TARDIS keys one by one, and the subsequent exchange in the TARDIS, were equally compelling.

The whole episode walks a bit of a line in teasing us this really could be the (an?) afterlife, and as far as I can tell it does so flawlessly. That the Doctor seems to believe he can find Danny in “hell” is slightly mysterious — perhaps he just means to convince Clara it’s impossible, or maybe he already suspects Danny’s death may not be exactly as it seems. The telepathic circuits are the perfect device for getting them to the 3W institute, and until writing this it didn’t occur to me to wonder why the Doctor didn’t check the coordinates and discover they were on Earth (perhaps the telepathic circuits don’t set coordinates).

Despite the grim mood, I found myself reminded of Douglas Adams at various points, particularly in the conversations between Seb and Danny. A bureaucratic afterlife isn’t the most original conceit, but it’s handled quite well here, with exactly the right mix of officious pleasantry and gray dismal void. The exposition of Danny’s “bad day” is about what you would have imagined, but again, handled very well indeed.

And then there’s the mausoleum, which looks terrific. All the clues for the second reveal are out in the open: the eye symbol (one of which looks like a large universe with a pocket universe bubble attached to it), the stacked “tombs,” and of course the presence of the Cybermen in the trailer. Still, reveal 2 was a serious thrill. I figured it out sometime after the mention of the “support exoskeleton” and before the elevator doors with the eyes on them, but many of you probably got it sooner. I loved the Doctor’s skepticism as the three words were explained, particularly his delivery of the phrase “freak out” and “Why? Is he an idiot?” Moffat has outdone himself with the way he simultaneously raises this spooky idea that the dead are conscious and sensate after death and allows the Doctor to quite reasonably scoff and shoot it down.

Missy (reveal 3) was of course exactly who we thought she was from the beginning, but again, this didn’t make it any less exciting to watch the Doctor figure it out. He clearly has an inkling; you can see it on his face at several points, particularly after he feels what must be her double heartbeat. Possibly her gender throws him off, or maybe he just can’t bring himself to believe she’s alive. I’d actually begun to doubt the initial theory and think it too obvious; and as soon as the Nethersphere was identified as a “Gallifreyan hard drive” (reveal 4, the one I didn’t see coming but which makes perfect sense in light of the way the Matrix (Doctor Who did it first, in 1976!) worked) I started to think “is this the Rani?” Certainly the technical nature of the scheme fits her modus operandi, Kate O’Mara’s performance and Michelle Gomez’s aren’t a million miles off, and the Rani was even called “Mistress” by some of her minions. But for Missy to be the Master works better than anything else would have, and of course it’s the next best thing to a female Doctor. I can’t wait to see the dialogue on this subject next episode.

I’m just scratching the surface here. I almost wish this weren’t a two-parter, because on its own “Dark Water” is without a doubt my favorite episode of the season. It’s riveting from start to finish, spooky and funny, ominous and powerful, moving and chilling. It seems scarcely possible for “Death in Heaven” to equal it, though “The Big Bang” was better than “The Pandorica Opens,” but as long as nothing happens to undermine the success of this setup, I’ll be happy.

Oh, and the Mistress’s escape plan next episode? Maybe “Missy” really is an android replica. You heard it here, folks.