Season synopsis
Contains spoilers for this season and earlier seasons.
In the summer of 1985, Starcourt Mall gives Hawkins a new gathering place, but Joyce notices magnets falling off refrigerators after a town-wide power surge. Her investigation with Hopper leads to a hidden Russian base beneath the mall, where scientists are trying to reopen the gate to the Upside Down. At the same time, Nancy and Jonathan trace strange rats and missing chemicals to a new Mind Flayer attack. Billy Hargrove and other townspeople become its hosts; the possessed gather into a huge creature made from melted animal and human bodies.
The danger pulls the teenagers into separate parts of the mall mystery. Scoops Ahoy coworkers Steve and Robin, along with Dustin and Erica, decode a Russian message and descend into the underground facility. Hopper and Joyce enlist Murray and the captured scientist Alexei to reach its control room. Meanwhile, Eleven and Max investigate Billy’s behavior and help the group track the Mind Flayer, though Eleven is wounded and her powers begin to fail. Dustin reaches his girlfriend Suzie by radio, and her answer to a code problem gives the adults the numbers they need to open the machine’s safe.
At Starcourt, fireworks give Eleven time to reach Billy through a memory of his mother. He breaks free of the Mind Flayer and dies protecting Eleven and Max. In the Russian control room, Hopper is trapped beside the gate machine after defeating its guard; Joyce turns the keys to destroy it, closing the gate and collapsing the monster. Hopper is missing, and Joyce, Will, Jonathan and Eleven leave Hawkins for California. Eleven cannot use her powers while packing, and Joyce finds Hopper’s unsent letter, which gives Eleven a final message from her adoptive father.