The plan to destroy Vecna and the Upside Down once and for all is simple at first — well, as simple as something on this show can get. Eleven, Kali, and Max will use their combined skills to enter Henry’s mind and kill him there; Dustin, Steve & Co. will venture to The Abyss to disentangle Holly and the other kids from the hive mind; and when everyone is out of there safely, Hopper will make the entire Upside Down go ka-boom with a lot of C-4.
Well, only some of that happens the way it’s supposed to. The C-4 part, pretty much. In the interim, there’s a lot of mind-hopping among Eleven, Max, Henry/Vecna, and even Will — and when Henry eventually finds the courage to go into the cave that had long terrified him in his own mind, it briefly seems that he might never be truly vanquished. Plus, one of the gang’s greatest assets — the ever-powerful Kali — sadly dies when Lt. Akers shoots her in the stomach after the military briefly gets her, Eleven, and Hopper in their grasp.
And oh, it gets worse. We’ve all been so concerned about Vecna, his hive mind, and the imminent collision of The Abyss and Hawkins that we sorta forgot about the Mind Flayer — and it turns out Vecna and his hive mind are inside the Mind Flayer. That freaky-looking tree that’s been in Will’s vision? Yep. Dormant Mind Flayer. And it isn’t dormant anymore.
Fortunately, Will, Eleven, and all of their friends don’t have any fear left to spare in these life-or-death scenarios, so they fight as hard as they can in The Abyss to destroy the Mind Flayer for good. Nancy, Steve, Robin, and the rest of ’em go to work on the Mind Flayer’s exterior, shooting it with bullets and fire and everything else in their arsenal. Meanwhile, inside the creature, Eleven uses her well-honed powers to face Vecna at last and rip him apart, impaling him on something spiky in the Mind Flayer’s insides. (Will helps out here, too, taking remote control of Vecna so the Big Bad and his tendril-like arms can’t do any damage to Eleven.)
After a massive battle scene worthy of the movie screens where this finale is showing across the United States, the Mind Flayer is toast, the kids are saved from the hive mind, and Vecna is within an inch of his life — and Joyce, in a well-deserved moment of heroism, finishes the job by taking an ax to Vecna until his head falls from his body. Go, Joyce!
But hey, we’ve still got 58 minutes left in this finale, so something devastating’s gotta happen — and it does, just after the entire group has successfully driven across the threshold that exits the Upside Down and enters regular Hawkins. At that threshold, Hopper & Co. have their vehicles cut off by the military, and the vehicles are raided in search of Eleven, whom Dr. Kay still wants to seize. At first, it seems El might have made a successful escape… but then Mike spots her standing on the exact point where Hawkins meets the Upside Down. Before Mike can stop her, Eleven has entered his mind, and she confirms that she’s made the choice to end her life here; if she doesn’t, none of this will ever truly stop. They have a heartbreaking final conversation in Mike’s head, where they both express their love for each other and kiss one last time. And if you’re a sucker for flashbacks to earlier seasons, this finale must have gotten you good: Mike and El’s final chat is littered with scenes from their friendship and romance, including reminiscences of the first day they met.
After they’ve said their goodbyes, Mike returns to the scene in Hawkins, and he and the others are crushed to see El still standing at the portal to the Upside Down. The C-4 that Hopper previously set up in the Upside Down goes off at last, and the entire world is wiped away — and Eleven goes with it.