Spoilers for this episode.
Billy flees the steelworks and tries to call for help, but a vision places him before a crowd led by his own double. Back at the pool, he is feverish and troubled by violent impulses. When Karen tries to explain missing their meeting, Billy imagines attacking her, then tells her to stay away. The double's demand that he build something returns to him as his condition worsens in the sunlight.
Mike lies to Eleven about his grandmother to avoid admitting Hopper threatened him. Eleven asks Max for advice, and the girls go shopping at Starcourt. Mike arrives with Lucas and Will to find an apology gift, but another clumsy explanation prompts Eleven to break up with him. Elsewhere in the mall, Dustin reunites with Steve and brings him the Russian recording. Robin helps translate it, while Steve recognises its background music from a nearby mechanical horse ride.
Nancy and Jonathan investigate Mrs. Driscoll's report and photograph a rat that has been eating fertilizer. After their visit, the animal dissolves into a crawling mass. Joyce seeks Mr. Clarke's explanation for her failing magnets instead of meeting Hopper for dinner; he describes the powerful electromagnetic machinery such an effect would require. Hopper meanwhile faces protests over Starcourt at the mayor's office. At the pool, Heather checks on Billy, who attacks her and takes her to the steelworks, where a creature emerges toward her.