Dr. Alexei reveals what the Soviets have been building, and Eleven sees where Billy has been. Dustin and Erica stage a daring rescue.
This episode provides examples of:
- Air-Vent Passageway: Played straight, unlike before. The air vents are more than large enough for Dustin and Erica to sit upright in and they use them to sneak around the base. Possibly justified, given that the base is several hundred feet underground and they have to get enough air down there somehow.
- And I Must Scream: When the Mind-Flayer speaks through Billy to Eleven and tells her its plans to destroy everything, Billy tears up, showing that he's fully conscious during all of this and is horrified at what he's now a part of.
- Anguished Declaration of Love: While Eleven is seemingly out of earshot, Mike talks himself into a rage telling the group that they should stop objectifying her. He finishes with "I love her and I can't lose her again" which was a bit more than he was planning to reveal. This earns him a moment of Stunned Silence from the group.
- Arbitrary Skepticism: Played for laughs: Erica believes everything Dustin tells her about Eleven's powers, sealing the gate, etc., but not the fact that her brother was involved.
- Batman Gambit: Hopper lets Alexi have the keys to his cuffs and the car, risking him escaping unscathed... but reasons that, should he actually go back to his allies in that state, there will be grievous consequences for him. Bauman and Joyce start to panic once they hear the car start up, but Hopper's gambit comes through when they see Alexi having stopped at the fence before backing up and getting out.
- Both Sides Have a Point: Max is right that Mike shouldn’t stand in the way of El making her own decisions. However, Mike’s concerns for El’s safety turn out to be 100% justified, especially considering what happens in the next two episodes — concerns Max brushes aside, apparently regarding El as invincible.
- Big Damn Heroes: Dustin and Erica create a distraction and break into the chamber where Steve and Robin are being held prisoner and rescue them, knocking out the doctor/torturer in the process.
- Bilingual Bonus:
- When Robin spits in the General's face, he calls her a bitch in Russian.
- The title itself is Latin for "out of many, one", It references both the 4th of July setting (being the motto of the United States) and the Mind Flayer building a larger physical body out of the melted remains of the Flayed.
- Bullying a Dragon: The Mayor learns you don't shame and disparage a uber-human Soviet with strong fists.
- Cassandra Truth: No matter how many times Steve and Robin tell the Soviets that they're not spies and found the base mostly by accident, they're not believed, even after they've been dosed with a truth serum.
- Continuity Nod: El looking at a box of Lucky Charms makes her remember her mother's visions of the Rainbow Room.
- Conveniently Coherent Thoughts: Billy's childhood memory of himself and his mother on the beach is detailed and coherent when probed by Eleven. Later, she happens upon more of his memories, which become a little less coherent due to being in the midst of the wind storm made by the Mind Flayer.
- Cooldown Hug: Mike pulls Eleven into one after she escapes Billy's mind screaming at the top her lungs.
- Curse Cut Short: At the sight of the Mind Flayer's hospital avatar, Max starts to say, "What the f—" and is cut off when the monster and Eleven go at it.
- Deadly Rotary Fan: Erika and Dustin encounter one as they pass through the Air-Vent Passageway. Dustin deactivates it by ripping out the wires from its control box.
- Destination Defenestration: El kicks the mini-Mindflayer's ass with her Psychic Powers before hurling it out a window. This still isn't enough to properly kill it, and it manages to escape by using a grate in the ground to retreat to the sewers.
- Dream Within a Dream: Eleven thinks she properly exited her Journey to the Center of the Mind of Billy only to find herself in another layer of the vision, again with Billy.
- Entertainingly Wrong: Subverted. Hopper explains to Joyce and Murray that Alexei is scared and would rather stay with them than to run back to his folks, all the while Alexei outside is stealing their car to get away from them...only for Hop to be proven right all along when Alexei can't go through with it.
- Fighting from the Inside: Heavily implied with Billy during his possession by the Mindflayer; while the Mindflayer is using his body to intimidate El by telling her its plans, a tear escapes one of his eyes.
- Fin Gore: Narrowly subverted. Steven nearly gets a fingernail ripped off before Robin taunts the Soviet General about how they cracked their code, which distracts them long enough for an alarm to sound and for Dustin and Erica to rescue them.
- Gilligan Cut: Alexei says that the underground base is guarded by some of the strongest guards in Russia, making infiltration impossible even for Rambo. Cut to Dustin - a pubescent nerd with baby fat and a birth defect - scurrying through the infrastructure.
- Good Parents: Billy's mom was a sweet woman who was encouraging of her son surfing until the events of her divorce from his dad forced her apart from her son.
- I Need a Freaking Drink: Hopper needs a whiskey after learning from Alexei that the Soviets opened up the gate to the Upside Down again. Murray can only offer vodka which Hopper is happy to accept.
- Internal Reveal: Dustin tells Erica about everything that happened in the last two seasons but she doesn’t buy the idea her own brother Lucas was involved.
- Journey to the Center of the Mind: Eleven journeys into Billy's psyche to find the "source" of where the Mind Flayer is.
- Leaning on the Fourth Wall: Max remarks that it's unnatural for her brother to be inside all day on the Fourth of July. The season premiered on July 4th, 2019, and the viewers presumably spent all day inside binge-watching it.
- Men Are the Expendable Gender: The Soviets beat Steve into a bloody pulp to get him to tell them who he works for and how he found the base, but they conspicuously hardly touch a hair on Robin's head in all that time (she is only seen getting slapped once).
- Missing Mom: We meet Billy's mom in flashbacks and saw what forced her apart from Billy.
- Mushroom Samba: The Soviets' Truth Serum doen't have the intended affect, instead making Steven and Robin loopy and giggly.
- Nice Job Breaking It, Hero: The Mind Flayer, speaking through Billy, tells Eleven that she made a mistake going after it, because now it knows she and the others exist, and it can use this fact to properly manifest in reality with all the Flayed it has accumulated.
- No OSHA Compliance: The door to the fire escape stairs at the hospital is almost completely blocked by piled bags of construction material carelessly left around.
- Not So Above It All: Robin reveals to Steve that, behind all the snark and irreverence towards him, she was obsessed with how cool he was.
- Painting the Medium: Alexi's Russian is translated in the subtitles up until the point what he says exceeds Murray's knowledge of the language.
- Phone-Trace Race: Bauman is concerned that if Hopper stayed longer than a minute on the phone, they would be able to trace him.
- Oh, Crap!: Both Dustin and Steve have this reaction when they see that the Soviets are re-opening the Gate to the Upside Down. Later, both Joyce and Hopper react this way when Alexei tells them what the Soviets are doing in Hawkins.
- Point That Somewhere Else: Dustin tells Erica to watch out for where she is pointing that electrocution stick she found.
- Real Men Wear Pink: Not a "man" yet, the uber-nerd Dustin reveals to Erica that he watches the My Little Pony Tv Specials. Erica clearly thinks he's revealed his knowledge of the show by accident, and expects him to backpedal when she asks him how he knows so much about it, and is rather put out by his total lack of embarrassment over it.
- "The Reason You Suck" Speech:
- Robin gives one to the General, about how relatively easy it was for a bunch of kids to break the Soviet spy code.
- Zigzagged with Max and Mike. Max calls Mike out for being overprotective of El, accusing him of not trusting her and being controlling. Mike points out his concern is about El using her powers, which Max and the gang have been encouraging her to do despite the physical toll it takes on El and her penchant to prioritize the mission over her own safety. In the end, Max's speech is subverted because Mike was right: not only does El delve so deeply into Billy's mind that she briefly gets stuck there, she ends up letting the Mind Flayer know she's there, who then sets its sights on her.
- The Reveal: We finally learn what the Mind Flayer is using the Flayed for: it's causing their bodies to break down to organic components so that it can build itself a flesh and blood body in this dimension, thereby allowing it to directly attack and kill Eleven and the rest of the Party.
- Shock Stick: Dustin uses a cattle prod to stun the Soviet Torture Technician.
- Shout-Out: Alexei refers to Hopper as a fat Rambo. Hopper seems a ltitle offended by the comparison.
- Slow-Motion Fall: Eleven in the Dark Void Room when Billy lets go of her.
- Spiteful Spit: Robin spits in the face of the Soviet General.
- Sympathetic Adulterer: Billy's mom is implied to be this, as she started seeing another man to escape the abuse of her relationship to his father.
- Torture Always Works: Averted in a way that highlights how cruel the Soviets are. No matter what they do to try and force information out of them, to the point of a Truth Serum, Steve and Robin don't give them anything... because they honestly don't have anything to offer. They're not American spies, they're just average American teenagers that happened upon a Soviet base.
- Torture Technician: The Soviets have one of these.
- Truth Serum: The Soviets, assuming Steve and Robin are lying to them, shoot them up with a severely disorienting drug in hopes that they won't have the presence of mind to keep their cover stories straight. The General isn't happy when Steve continues to insist they just work at the mall.
- Up Close with the Monster: At the hospital, the mini-Mindflayer has Nancy at its mercy on the floor and roars into her face from inches away. Eleven saves her from death by psychically throwing the monster around, then out the window.
- Used to Be a Sweet Kid: During Eleven's Journey to the Center of the Mind, she discovers that Billy was a happy child who enjoyed swimming and loved his mother. His eventual turn to a violent bully was the result of watching her be regularly abused by his absolutely vicious father, then being forced to live with him once they got divorced.
- Voice of the Legion: Billy has a reverberating voice while talking to Eleven during her Journey to the Center of the Mind.
- Your Other Left: When Robin tells Steve to look to the right, he does the opposite so she tells him to look to the other right.
