We open to Eleven brushing her teeth at Max's, I think she's starting to suspect the Mind Flayer is in Billy. Max introduces her to Wonder Woman.
At Mrs. Driscol's the paramedics are taking her to the hospital while she screams "I have to go back!" Jonathan and Nancy are understandably freaked out. The ambulance drives right by the Steel Mill, where Billy and Heather have taken her parents. Tied up and gagged, they leave the pair for the Mind Flayer in the shadows, made up of dead rats. It shoots its tentacles down their mouths, presumably to brainwash them. It's one of the most disturbing scenes in the series so far, but it's going to get a lot worse. Cue credits.
Hopper wakes up and promptly vomits. He's in a lot of pain after getting his ass handed to him by Russian Terminator. Joyce has been taking care of him throughout the night. Joyce got the license plate of Russian Terminator, she and Hopper both think it's just a State Government Agent, boy are they wrong.
The boys are trying to get in touch with the girls over the walkie talkies, they have a Code Red situation. Max isn't having it and turns off the Walkie Talkie. So, the boys call her home phone and Mike's tone of voice seems to convince Max that something is up. The boys try to reach Dustin, but he doesn't pick up because he's observing the Russians. The Scoops Troop is trying to come up with a plan to get into the room the Russians are guarding. Robin seems to have an idea, because she grabs money from the tips jar and runs off.
At the paper, Jonathan and Nancy are called into Todd's office. He's angry at Jonathan and Nancy "breaking" into Mrs. Driscol's house, apparently, she's a paranoid schizophrenic. The woman's family is threatening litigation, and Todd fires the pair.
In the Wheeler's basement, the Party goes over the facts. Will tells them about feeling the presence of the Mind Flayer. Eleven doesn't understand because she closed the gate. Will puts up the proposition that by doing so, she locked the part of the Mind Flayer that was driven out of Will last season is now locked outside in the real world with them. Max is skeptical, but Mike says "we have to assume the worst. The Mind Flayer is back." This is one of the things I love about this show. The kids are smart, and they don't fall prey to the typical horror clichés. Will explains that the Mind Flayer would want to attach itself to a new host. Eleven asks how you could tell who is a host.
Hopper and Joyce arrive at Mayor Kline's office, he starts asking questions about the Russian Terminator, having found the license plate number from Joyce. Hopper remembers seeing the guy walk out of the building. This is a nice call back to season 1, Hopper is more observant than he lets on and can immediately tell Mayor Kline is lying when he claims to not know anything. Hopper cuts out the middle-man and just starts to beat the absolute crap out of Mayor Kline until he gets some answers. Kline finally spills out that the guy works for Starcourt Mall, which has been buying up property. Hopper asks where the records are.
Nancy and Jonathan have an argument in their car, Nancy is upset because no one believes her. Jonathan is upset because he doesn't have a job anymore and doesn't have the financial stability she does (apparently Ted Wheeler makes six figures). Their argument ends with them concluding they don't understand each other anymore, and one wonders if they have broken up. It's unclear.
Back at Starcourt, Robin has managed to buy a copy of the blueprints for the Mall. It turns out the air ducts lead to the room. The problem is none of them are small enough to fit through the air ducts.
At the pool, the party observes Billy doing the lifeguard thing. Mike thinks Billy is the host and comes up with an idea. The Mind Flayer doesn't like heat, so he plans to lock Billy into the Sauna and turn the heat up, either way, they'll know if he's the host or not.
Back at the mall, Scoop Troop tries to entice the services of Erica, Lucas' bratty, obnoxious little sister because she's small enough to fit in the air ducts. Erica, being a small burgeoning capitalist, demands to be compensated for her services. Her price is free ice cream for life. For as much as Erica annoys me, I won't lie, I loved this bit.
Joyce and Hopper arrive at Kline's manor with the mayor in tow, where he gives them the deeds to the land being bought by Starcourt. Joyce and Hopper realize the property that's been bought is all near the power plant.