The Upside Down is a Christmas episode of Stranger Things that debuted on Netflix on July 15, 2016.
After getting caught sneaking into the Hawkins Laboratory, Hopper and Joyce are being interrogated by Dr. Brenner and his men. Brenner reveals to Joyce that the scientists at the Laboratory do not understand the the Monster's behavior, and he needs her help to stop it. Joyce refuses and tells him to go to hell. In another room, Hopper reveals everything he knows about Eleven and the Laboratory's experiments. The agents threaten to inject him with drugs, however Hopper makes a deal with Brenner so that he and Joyce can find Will.
Nancy and Jonathan are off to find the monster and end it once and for all. The two are armed with weapons and set up a bear trap inside the Byers home to catch and kill it.
Meanwhile, Joyce and Hopper set off to find Will inside of the Upside Down, putting on special suits to protect their bodies from the toxic atmosphere. Inside the gate, Hopper recalls a memory of his late daughter, Sara, having trouble controlling her breathing after Joyce experiences some shortness of breath. Joyce and Hopper reach the Upside Down's version of Castle Byers, where Will was hiding when Eleven contacted him. The shack has been destroyed and Will is nowhere to be seen. Hopper notices a small stuffed lion laying on the ground. The toy triggers another flashback where the late Sara is holding a similar stuffed tiger as Hopper reads to her in a hospital bed, as she slowly dies from cancer. Back at the Byers house, Nancy and Jonathan attempt to lure the monster into the house with their blood. Steve then shows up in a panic to talk to Jonathan and make amends. He is surprised to see Nancy, who quickly tells him to go home, but after seeing Nancy's bandaged hand, Steve bursts into the house to see what is going on. Nancy pulls a gun on him and tells him to leave. He hesitates and the Monster breaks through the ceiling of the room Steve, Jonathan, and Nancy are in. They lead the monster towards the traps, but the Monster escapes.
Nancy and Jonathan stress that Steve should leave now as the Monster will come back. Steve leaves the house and gets into his car.
Suddenly, the lights flicker, signaling the monster is coming back. The monster pins down Jonathan, almost killing him, but Steve returns to the house and assaults the monster with Jonathan's baseball bat. The three lure the monster into the bear trap and light the monster on fire, but when the fire goes out, the monster is nowhere to be found. Mike is talking with Eleven at the school where they are hiding out. Mike tells El Ep8-Eleven and Mike2 Mike reveals his feelings for her. that everything will be okay, that his parents will take her in and she will be like family. Mike says she will not be like a sister to him, as he invites El out to the Snow Ball school dance and kisses her, revealing that he loves her. Brenner's men find the boys and Eleven hiding in the school. The agents corner them in the hallway, but El uses her powers to make the agents bleed from their eyes until they fall to their death. This drains El so much that she will not wake up. The boys are helpless as Brenner approaches Eleven and they are captured. Brenner promises Eleven that she would be brought back home. But Eleven sees through his facade and rejects, crying and reaching out for Mike. The Upside Down S01-E08 SS 006 The lead agent shooting the Monster Attracted by the blood, the monster suddenly bursts out of the brick wall. Brenner's men attempt to subdue the monster, but are unsuccessful. The monster attacks Brenner and seemingly kills him. Eleven and the boys are able to escape to a science classroom. Meanwhile, Joyce and Hopper have tracked the wounded monster to the public library in the Upside Down. There are bodies of humans who have been taken along the shelves with vines and tendrils surrounding them. Joyce and Hopper find Will with a tendril extending down his esophagus.
Back at the scho Ep8-Mike and Lucas Mike left in tears as Eleven vanished. ol, the lights start flickering as Mike talks to Eleven. Mike promises to go to the school dance with El, as the monster storms in the classroom. Lucas takes out his slingshot to stop the monster. Before the monster gets too close, El, despite being drained, summons enough power to pin the monster against a wall. El looks back at Mike and says "Goodbye Mike" before using all her power to disintegrate the beast's body into a dark thick mist, vanishing inside it. Mike was left in tears as the kids frantically looked for her in the classroom but in vain. The Upside Down S01-E08 SS 007 A tendril inside Will's throat In the Upside Down, Hopper and Joyce preform CPR on Will. Hopper recalls a memory where he watched Sara die in the hospital as the doctors try to use CPR to revive her. Hopper is pounding on Will's chest to start his heart again until he gasps for breath. Joyce and Hopper breathe a sigh of relief. Will is recovering in the hospital where Joyce, Jonathan, Mike, Lucas, and Dustin all see him and fill him in on all the surprising events that had happened while he was gone. As Hopper leaves the hospital, he is stopped by a car which signals him to get in.
Eleven wishes Mike "goodbye" before proceeding to kill the Monster One month later, the four boys are playing Dungeons & Dragons in Mike's basement. Mike still has Eleven's basement fort set up in perfect condition in her memory and clearly misses his lost friend. Jonathan arrives and picks up Will from the Wheeler home. While Jonathan and Will are leaving, Nancy gives Jonathan a Christmas present and a kiss on the cheek. Will opens the present in the car, and it is revealed to be a camera. Nancy is then seen with Steve, and he asks if she gave Jonathan the present. Later, Hopper ventures out into the woods and places some eggo waffles in a snow-covered box in the forest.
Will's sudden return to Upside Down Back at the Byers house, Joyce, Jonathan, and Will are enjoying their family dinner. Will excuses himself to go to the bathroom to wash his hands, where he actually coughs up a black slug into the sink, and he momentarily phases into the Upside Down. The lights flicker again, and Will is back in his world. He returns to dinner with his family, but doesn't disclose the event to them.