In 1984, a team at what appears to be Hawkins Labs fiddle with a machine that looks like it's meant to crack open the Gate to the Upside Down. But it's not the team at Hawkins — it's their Soviet counterparts, up to the same mission they were on. Turns out, the Cold War includes interdimensional science too.
The timeline jumps ahead this season to the Summer of 1985, again over the course of just a handful of days. Steve, Nancy, and Jonathan have graduated, and while Steve is stuck working at an ice cream parlor with sarcastic co-worker Robin, Nancy and Jonathan have landed gigs at the local paper. But parts of Hawkins are in a decline — and not just because of some eerie power outages: a mall arrives in town and much of the town's hometown stores are deserted as a result. Last season's bully Billy gets sucked into the Upside Down and emerges with an altered personality, courtesy of the Mind Flayer, who's up to his old tricks in Hawkins. Dustin, Steve, and Robin figure out that the mall isn't just a mall: it's a secret base for Russians. And Nancy and Jonathan's bosses? They're possessed by the Mind Flayer now too, just like Billy.