We open to the sound of a growl, and Hopper standing at the quarantine zone’s edge, where he has a vantage point to see the young demogorgons enter the lab, directly coming back to Episode six’s cliffhanger. We see a demogorgon emerge and stare at Harper and go through the glass, with obvious intelligence as it tracks back and forth between Hopper and Owens. It proceeds to try to slam into the glass and enter the facility, but Owen assures Hopper the creature can’t get through, which obviously means it will- it just needs a little help from it’s friends. Now with help, the poly-carbonate window no longer seems like such a challenge. Owen hits an alarm.
We drop back to Will, who now knows it’s too late. The scientists vacate the control room, with Hopper and Owns heading upstairs instead of into the elevator. Likely, they know what happened to the first scientist who tried to make it to the elevator instead, and it’s a nice call back to season one. Nameless scientists head for the elevator with demogorgons hot on their heels.
Mike suddenly tells Joyce that they need to make Will sleep; because the shadow monster can use him as a spy. He tells Joyce that if they make him sleep, he can’t spy, to which Will begins to freak out and scream he’s lying.
Hawkins lab is in a panic; the demogorgons made it into the elevator with the scientists, and are now on the floor with Will who doesn’t know who Joyce is, and they opt to make him sleep. It’s an emotional few minutes as Will fades out of consciousness, and Hopper and Owens suddenly burst in with demogorgons hot on their trail. Hopper grabs will and Mike, Will, Hopper, Bob, Joyce and own flee; though they find only that they can hide in a new room which turns out to be the security room. They have a view of the many demogorgons trying to kill the staff, until the lights are suddenly cut. Surrounded by demogorgons it seems they are truly trapped.
After credits, we cut to Max’s mother and step dad returning home, to find Max is gone, her window open. Billy is in his room, getting dressed and doing his hair. Susan tries to talk to him and Billy rebuffs them. Both parents ask him where Max is- and Billy doesn’t know where she is, and is angry that they have been three hours late. His father accuses him of staring at himself in the mirror and being a faggot; which may point to Billy’s hyper-masculinity problems. Billy’s father pins him against the wall, and begins to hit him. Neil, Billy’s father is aggressive and tells him he will be canceling his date and going to find Max. Obviously, Billy is going to take it out on Max, and angry tears run down his cheek.
We cut to Dustin, who is still with Steve, Max and Lucas. They discuss Dart and his markings, and the molts he’s done. Steve brings up the fact that Dart ate Mews, and Lucas confronts Dustin in his lie that he hadn’t kept Dart, when he had. Lies divide the party, and Steve steps away, distracted by something. He pulls the gang’s attention away because he’s found something. Only Max is smart enough to question why they’re going to head towards the screeching sound.
The gang emerges on a field, of mist, with the screeching still evident. They can see the Lab, and Lucas realizes the lights out lab means that the demogorgons have headed home.
Cut to Mike and company, Dr. Owens is detailing a map to show an escape, though someone will predictably need to go down to the breakers and reset them. Hopper takes the map, eager to head into danger when Bob stops him, explaining why he can’t. Bob decides he will go because he is the only one who knows how to reset the security. Joyce embraces him, and likely for the last time.
Hopper and Bob head out and collect supplies from soldiers; grabbing guns and walkies. Hopper gives Bob a run down of how to use a gun. They go their separate ways, and Bob tells Hopper not to wait for them.
Nancy and Jonathan show up at the lab, unsure of what is going on, other than the electricity is off. They know something is wrong, and Nancy says she thinks something is wrong. Something is in the woods- upon inspection they find Steve, Dustin, Lucas and Max. They are about to explain what they’re all doing there when the demogorgon screams sum it up pretty well.
Meanwhile Bob heads down to reset the breakers, cautiously picking his way down the stairs. A steam pipe screeches above him, adding more tension and drama to the moment. Bob finds more bodies, further highlighting the danger he is in. Despite this, he continues on and manages to reset the breakers and restores power to the lab. Will & co can now see everything that’s happening on the monitors.
Meanwhile, Nancy and Dustin’s group realizes the power is now on, and rush to get inside the lab though the gate still will not open for them. Dustin can’t get the the gate open to allow the group inside, and there is a rising sense of urgency.
Inside, Dr. Owens speaks to Bob through the comms system. Bob begins to work on setting the locks to open. He manages to unlock the doors, and Hopper’s group can now escape. Of course, he opens the door and allows Nancy’s group in without knowing it. Hopper is impressed, and Bob says he’ll meet them outside. They watch as a demogorgon comes down the stairs towards Bob, who has an idea and turns the sprinkler system on, deterring the demogorgon. Dr. Owens is impressed, and tells Bob to go. He does, but forgets his gun.
As Hopper grabs Will and prepares to evacuate him, Mike and Joyce, Owens gives him a walkie-talkie and tells him to go. Owens plans to stay behind and watch the camera, to let Hopper know of any trouble, which effectively will seal his death. Hopper leaves, holding Will in one hand and a gun in the other. They escape the front doors but Joyce hangs back, hoping Bob will show up.
We cut to Bob, who Owns is trying to guide towards the exit. Owens guides him to take the next right, down a corridor lined with bodies. The tension intensifies when Owns finds a demogorgon coming around a corner and tells Bob to stop. Owns tells Bob to get in a closet to his left, and though Bob asks questions he gets in the closet. The demogorgon sniffs around the door, and Bob is obviously terrified. The demogorgon moves on, and Owens and Bob take a moment to sigh in relief. Owens tells him he has a clear shot to the front door, encouraging Bob to make it out.
Bob opens the closet and is almost home free when a broom drops, and Bob turns to see the demogorgon that had just past him clearly hears the sound of the broom too. Owens tells Bob to run, and in a chase sequence Bob tries to make it to the front door with the demogorgon on his heels. He makes it to the foyer and sees Joyce, relieved before a demogorgon attacks him. He fights as best he can, and Joyce watches as the demogorgon attacks. Hopper tries to save him, shooting and wounding the demogorgon when they break down the door and begin to attack. Hopper realizes they are outnumbered, and has to drag a bereft Joyce Byers out of the building.
Bob dies, reaching for Joyce one last time.
The demogorgons attack the door trying to escape when Jonathan shows up in his car, telling the group to get in. The car comes streaking around the front followed by Hoppers’ truck. Hopper instructs Max, Steve, Lucas and Dustin to get in. They drive away, and we cut back to the demogorgons feasting upon Bob.
They return to the Byers home, where Will is still sedated. The group doesn’t know what to do; Hopper having tried to find help in the National Guard. Hopper then retreats to Joyce’s room to see her, with Will’s tunnels still taped up everywhere. Joyce is in shock, having lost Bob. Everyone has a down time where they all realize what they’ve lost, as they wait for a phone call that will likely never come. They mourn Bob and all he’s tried to do, having been the hero they needed.
Mike tries to rally the gang, and Dustin comes up with a name for the adolescent demogorgons, dubbing them demo-dogs. Mike begins to plan how to defeat the Shadow Monster, who connects Will to everything else. The Shadow Monster is the center of the hive mind, and Lucas comes in with the episode’s title- the Mind Flayer.
Dustin explains that the Mind Flayer is a monster from another dimension, and Hopper seems unimpressed with the idea. Dustin struggles to get the point across that it is simply an analogy to understand what the Shadow Monster is. Dustin explains it wants to destroy other races, and the destruction of their world as they know it. They hatch a plan to kill the Shadow Monster- which in turn will kill everything else.
Joyce emerges, and details that they need to figure out what is going on and kill it. Mike says Will is their answer, though Will can’t be trusted as he is a spy for the Mind Flayer/Shadow Monster now. Hopper and company begin to empty out the shack Will hid from the Demogorgon in season one, and Nancy and Steve begin to put up black tarp. They have a moment, and Nancy tells Steve that his help was ‘really cool’ and they bond over the trouble that the children seem to bring.
We cut to Dustin, who apologizes to Lucas for his lies over Dart. Dustin is perturbed that Max and Lucas have bonded, and though Lucas denies it, Dustin tells him that he feels the electricity. We cut to Max who tries to connect with Mike over Ele. Mike is still pushing Max away, and over Eleven who Mike still terribly misses. He still believes that the demogorgon took Eleven, and has no idea Hopper knows where she is.
We cut to Joyce and Jonathan who expresses doubt, and Joyce thinks her son is still there. They continue to make the shack a safe zone where Will can’t possibly know where he is. They cover every surface, and Jonathan brings will Outside. They strap will down and tie him to a chair, instilling only lights and a chair opposite. Preparations complete, Joyce and Hopper wake Will.
Dustin is back in the house, pacing as the rest of the gang sits and waits anxiously. Max is concerned that Will can send the demo-dogs after them, and Lucas tells her that he won’t- and that if he does, it’s judgment day.
Cut back to Will who is disoriented and can’t understand why he’s tied up, with Hopper, Joyce, Jonathan and Mike watching him struggle. Joyce tries to talk to him, but Will becomes increasingly terrified that he is tied up. He begins to scream, and lights begin to flicker upon the request that he identifies the Shadow Monster. Eventually, Will runs out of energy and the lights stop, as does his screaming.
Joyce sits across from him, detailing memories that matter to them. Jonathan reaches for the painful memories of Dad leaving, and that they’d built Castle Byers after that, and how it had taken so long because Will was terrible at hammering. Mike reaches for their first meeting, in kindergarten, when he was alone and scared but Will had been there for him. They try to reach him with the memories that matter- memories that mean something to him, trying to reach Will, deep inside.
Will reacts by telling them to let him go, and Hopper realizes he is communicating in Morse code by tapping his hands. Will is still in there; trying to communicate via Morse Code. Jonathan grabs a CD player and tries to use each memory to give Will a chance, who uses Morse Code to communicate.
They finally get the message that Will has sent-
Suddenly the phone rings, and Will now knows where he is, and the Mind Flayer does too. They put Will back to sleep but it is too late- the demo dogs are on the way. They have to make a quick escape, and head into the house to grab weapons and bunker down into, screeching heard in the distance.
Hopper, Nancy and Steve arm up and square off to defend the kids, Joyce and company, ready for the danger incoming. They hear the demo-dogs, and see the bushes rustling, but can’t tell why they haven’t attacked. There is screeching heard outside, though a different sort. As if the demo dogs are being attacked.
Finally, a demo dog flies in the window- but it is dead. Hopper is the first to realize this, and realize that someone is at the door.
Everyone is prepared to fight as the locks are psionically open, and Eleven finally makes an appearance. Stepping into their life in a new wardrobe and with a new purpose, the girl that most everyone hasn’t seen in over a year is here to save the day.
We close with Mike and Eleven recognizing each other.
With the gang reunited, how will they now face the demo dogs, and what will the future hold? We’ll find out on the season finale, The Gate.