Researchers at Hawkins National Laboratory open a rift to the "Upside Down", an alternate dimension that reflects the real world. A monstrous humanoid creature escapes and abducts a boy named Will Byers and a teenage girl. Will's mother, Joyce, and the town's police chief, Jim Hopper, search for Will. At the same time, a young psychokinetic girl who goes by the name "Eleven" escapes from the laboratory and assists Will's friends, Mike Wheeler, Dustin Henderson, and Lucas Sinclair, in their efforts to find Will.
When a young boy disappears, his mother must confront terrifying forces in order to get him back.
Lucas, Mike and Dustin try to talk to the girl they found in the woods. Hopper questions an anxious Joyce about an unsettling phone call.
An increasingly concerned Nancy looks for Barb and finds out what Jonathan's been up to. Joyce is convinced Will is trying to talk to her.
Refusing to believe Will is dead, Joyce tries to connect with her son. The boys give Eleven a makeover. Nancy and Jonathan form an unlikely alliance.
Hopper breaks into the lab while Nancy and Jonathan confront the force that took Will. The boys ask Mr. Clarke how to travel to another dimension.
A frantic Jonathan looks for Nancy in the darkness, but Steve's looking for her, too. Hopper and Joyce uncover the truth about the lab's experiments.
Eleven struggles to reach Will, while Lucas warns that "the bad men are coming". Nancy and Jonathan show the police what Jonathan caught on camera.
Dr. Brenner holds Hopper and Joyce for questioning while the boys wait with Eleven in the gym. Back at Will's, Nancy and Jonathan prepare for battle.