Under the mall, Steve and Dustin recognize the gate and immediately realize the situation is worse than they thought. Suddenly the alarm starts to blare as the base now knows they've been infiltrated. Steve and Robin hold a door closed long enough for Dustin and Erica to escape via the vents but they're both captured as a result. That said, it speaks to the bravery of these two characters that they put the lives of the kids above their own. Especially since Robin doesn't have the close relationship with Dustin that Steve does.
Back at the hospital, the gang in the waiting room realize something isn't right; the lights are flickering, and Will senses the Mind Flayer. The blob-like flesh creature roars at Nancy and we get a good look at its maw. Its open mouth is full of teeth made out of bones! The bones from Tom and Bruce. The creature starts to chase Nancy, Jonathan tries to get the creature's attention to lure it away from Nancy, he is unsuccessful. Nancy locks herself in a room, but the creature turns back to goo and squiggles underneath the door. Jonathan is in a complete panic as he tries to break through the door and get to Nancy before the creature can kill her. As tense as this scene is, it's touching to see how much these two care about each other. The kids decide to take matters into their own hands and start heading up the stairs, ignoring the nurse who begins to yell at them. The creature knocks Nancy around as Jonathan continues to try breaking through the door. Right before it can kill her, the kids arrive and Eleven manages to throw it out the window. It lands in the parking lot, and the party can only watch as it slithers down a storm drain and into the sewers, leaving behind the bones too big to fit through the drain. It makes its way to the Steel Mill where it joins with the Mind Flayer, also made from the same goo. Billy says, "it's time." Cue opening credits.
Somewhere in Hawkins, we find sleazy Mayor Kline overseeing the 4th of July fair being set up. Russian Terminator arrives to have a talk. Kline claims to have people out looking for Hopper, but her gets a bit too cocky and insults Russian Terminator, it goes as well as you'd expect, and Russian Terminator informs Kline he has one day to find Hopper. He really sounds like Arnold Schwarzenegger in this scene.
Back at Murrays compound, Hopper arrives with Burger King (YAY PRODUCT PLACEMENT!) Alexei doesn't want to cooperate because he asked for a Cherry Slurpee, and Hopper got Strawberry. We get a very funny back and forth about it. Although Hopper's temper is getting the better of him, its funnier here, but it's less funny when you remember his behavior towards Mike and Eleven. We also learn that Alexei is fond of the cartoon Woody the Woodpecker. Eventually a frustrated Hopper throws Alexei out of the compound and gives him the car keys, so he can get his own Slurpee. He believes Alexie won't try to escape, because otherwise he'll be killed by his own side and knows this. Alexei promptly escapes from the cuff, jumps into the car, and then doesn't leave. It turns out Hopper is right.
Underneath the Mall, Dustin and Erica are hiding in the air ducts, and we arrive just as Dustin finishes telling Erica the whole story of the last two seasons. She believes everything about the gate, the demodogs and Eleven being psychic, but she doesn't believe that Lucas was there. Erica continues to be a brat, but accidentally reveals how good she is at math. Dustin says that makes her a nerd. Meanwhile Steve and Robin are being interrogated, mostly Steve. And by interrogating, I mean getting the crap beaten out of him by a giant Russian. They keep asking him who he works for, and ironically, it's the truth that gets him beaten up. The Russians don't believe that he works for Scoops Ahoy. Steve and Robin are tied to chairs and left alone in a room, but Steve is out cold from the torture. Yeah, this is DARK.
El is doing her thing, looking for disappeared people. Based on the amount of bloody tissues we see, she's been at it for a while. Mike is freaking out over how long she's been using her powers for, afraid she'd going to get hurt or worse, and arguing with Max about it. Nancy tries to follow up about the diseased rats but is having no luck. Max asks Nancy and Jonathan to settle an argument over who should set El's limits, Mike or Eleven. Mike is angry with the question, pointing out that no one knows what her actual limits are and she's putting herself in danger. This is a fair point, no one actually knows what the limits of Eleven's powers, and I'd argue his frustration here comes from a place of genuine concern, not trying to control El like Max thinks he is. As Mike gets more frantic and upset, he finally blurts out the truth, "because I love her, and I can't lose her again." The whole party has an "oh shit," look on their faces, Max in particular. I think in Max's case, she's been super critical of Mike all season and didn't really believe he loved Eleven that deeply. He clearly does, although you can tell he's a bit embarrassed afterwards. But when you think about it, it makes sense she didn't believe him until this point. Her stepdad and her stepbrother are both violent, abusive jerks, and we never learn anything about her dad, but I think it's a safe bet her mother divorced him. So, she doesn't have a role model for a healthy relationship. At that moment El emerges from her room to say, "I found him."
Back at Murray's, Alexei is spilling his guts; the Russians are building a gate to the Upside Down. They needed to build where the barrier was weak because it had been opened in Hawkins before. Now Hopper and Joyce understand that the situation is worse than they thought. Murray asks if the gate can be closed, Alexei confirms that it can be, but it can't be reached because its guarded and breaking in is impossible.
So naturally we cut to Dustin and Erica making their way through the underground facility. They emerge into a room full of the green stuff that melts through the floor. Dustin finds the keys for a cart and Erica finds a cattle prod like the ones in Jurassic Park. In the room, Steve finally wakes up. He's taken one hell of a beating. Steve and Robin use the "Indiana Jones tied to a chair hop" to try and reach a pair of scissors but fall over. The two end up talking about high school, it turns out they shared a class, but Steve never noticed her. Robin admits she was obsessed with Steve, because as she tells him, even the losers who act above it want to be popular. Steve tells her popularity isn't all it's cracked up to be, and how it's not that important. It's really incredible how much Steve has evolved as a character. He was the MVP of Season 2, and he continues to grow more mature, and is even a little bit wiser then he's given credit for. Props to Joe Keery for taking the jerk jock stereotype character and making it something special. Also Props to Maya Hawke who avoids the usual pitfalls of a new main character, and instead gives a performance that jives really well with Keery's. The Russians return with a doctor who injects Steve and Robin with a "truth serum."
Eleven has found Billy, he's staying inside his room on the 4th of July, which Max assures the party is not normal. El has a flashback to finding her Mom last season, which gives her an idea. She's going to try and reach Billy the same way. Mike isn't happy with it, but he accepts it when El asks him to trust her. El does her thing and we see Billy sitting on his bed. There's a blink and you miss it continuity error here. Billy grabs El and she falls backwards, landing on a beach. She's reached Billy's memories. First, we see Billy as a kid surfing at the beach, his mom watches. She's very proud of him. Eleven sees a storm in the distance.
Hopper calls a number that Dr. Owens gave him last year. The gate is open, and he needs backup. But he also gives away Murray's number, compromising him. Murray is pissed that he'll have to relocate. Joyce calls the number back and chews out the guy on the other end, explaining how urgent the situation is. It's very funny. The whole group leaves for Hawkins.
Steve and Robin are starting to get loopy from the drugs they've been injected with. They spill the truth, and it's what they've been saying all along. The General is not amused, and he doesn't believe them until the alarm goes off. The alarm makes the same noise as the alarm on the second Death Star in Return of the Jedi. Once the general leaves the room, Dustin runs in and hits the doctor with a cattle prod, and now he probably has a kill count.
Eleven walks towards the storm, seeing more of Billy's memories. We see Billy and his mom being abused by his Dad. Eventually it gets so bad that his mother leaves. Billy takes out his rage on other children. In the center of the storm Eleven reaches the Steel Works. The gang looks up the address in the Yellow Pages (Remember those?!). Mike urges El to get out. El removes her eye covers, but everyone is gone. Billy appears, she's in his. Billy gives the chilling monologue we got in the final trailer. Across Hawkins the Flayed just leave what they're doing and head towards the Steel Mill. They walk into the basement and melt into goo, joining with the Mind Flayer, its gross and disturbing. It's also where the episode gets its title. E Pluribus Unum, out of many, one. During the monologue, a single tear falls from Billy, a clue that he's still in there, somewhere, and doesn't want to do what he's being made too. El pulls off the eyewear for real and instantly clutches Mike, terrified and in tears. The Mind Flayer, now something like thirty feet tall, emerges from the Steel Mill. Cue end credits.
This is getting DAAAARK, and yet it's still funny. Mike admitting to everyone (except El) that he loves El, is easily this episode's highlight.