It all started in a lab run by Dr. Martin Brenner (Matthew Modine). There, children of various ages participate in a series of tests and experiments to unlock their psychic power. One of Brenner’s subjects, named Eleven (Millie Bobby Brown), learned to use his full power with the help of the kind yet enigmatic Henry Creel (Jamie Campbell Bower). But it turns out that Henry has plans of his own and a vile reason to help the child.
Fast forward to the present time. It’s March 1986, eight months after the Starcourt Mall incident. Eleven now lives with the Byers in California and is currently attending high school after losing her power and her foster dad, Jim Hopper (David Harbour).
However, a powerful child like Eleven can not simply outrun her past as easily as that. Soon enough, Dr. Brenner and Dr. Owens (Paul Reiser) show up on her doorstep to convince her to regain her power to fight a new evil brewing at Hawkins. She agrees, and they take her to a super secret facility at the heart of a barren desert.
After Eleven’s departure, Mike Wheeler (Finn Wolfhard), Jonathan (Charlie Heaton), and Will Byers (Noah Schnapp) got themselves entangled with the cops. But with the help of Jonathan’s friend Argyle (Eduardo Franco), they managed to work their way around the authorities to come after Eleven. With no clue where to go, they detour to Dustin Henderson’s girlfriend, Suzie (Gabriella Pizzolo), to find El’s location. As they race against time and the police, the evil lurking gets more powerful by the moment.
Back at Hawkins, Max Mayfield (Sadie Sink) struggles to move on from the death of her brother. Nightmares, headaches, and nosebleeds. Max seems like she’s experiencing signs of trauma or prolonged guilt and grief. But when a group of teenagers, experiencing the same things, end up dead, something is definitely afoot. Even though the authorities suspect that it was the eccentric student Eddie Munson (Joseph Quinn) who killed them, the manner of their death is very unnatural. Max knew it was far more wicked than a high schooler. So she enlisted the help of Steve Harrington (Joe Keery), Nancy Wheeler (Natalia Dyer), Robin Buckley (Maya Hawke), Dustin Henderson (Gaten Matarazzo), Lucas (Caleb McLaughlin), and Erica Sinclair (Priah Ferguson) to help her identify what it is.
Meanwhile, Jim Hopper, the hero of the Starmall incident, was presumed dead by Hawkins authorities. But it was revealed that the Russians kidnapped and tortured him, partly because of his involvement in their experiment on the Upside Down. During his time in prison, he got a little help from one of the guards, Enzo (Tom Wlaschiha), to send a message to Joyce (Winona Ryder). Upon learning that Jim was alive, she asked her friend Murray (Brett Gelman) to join her and save him in Russia. They traveled to Kamchatka only to discover the Russians' sinister plans for the Demogorgons and the Upside Down.