Spoilers for this episode.
Will's warning brings the children together to compare what they know about the Mind Flayer. Eleven's vision makes Billy their main suspect, while Max struggles to believe her stepbrother is possessed. Remembering the creature's hatred of heat, they decide to trap Billy in the pool sauna after closing. At the steelworks, Billy and Heather have already delivered Heather's parents to the creature, and its control is spreading through Hawkins.
Nancy and Jonathan lose their newspaper jobs after Tom dismisses their investigation into Mrs. Driscoll. The argument that follows exposes their different worries about money and being taken seriously. Encouraged by her mother, Nancy returns to the hospital. Hopper recognises the motorcyclist's link to the mayor and forces Kline to explain Starcourt's purchases of nearby properties. At the mall, Robin obtains building plans, and Erica negotiates free ice cream in exchange for entering a guarded storage room through its ventilation shaft.
The sauna's rising temperature brings out dark veins and unnatural strength in Billy. He pleads with Max, then breaks free and attacks Eleven. Mike intervenes when Billy has her by the throat, giving her time to throw him through the wall. Billy escapes to Heather and a room full of other possessed residents. Nancy sees Mrs. Driscoll convulsing during the confrontation. Meanwhile, Erica lets Dustin, Steve and Robin into the storage room, where glowing cylinders surround them. The room suddenly descends: it is an elevator.