A frantic Jonathan looks for Nancy in the darkness, but Steve's looking for her, too. Hopper and Joyce uncover the truth about the lab's experiments.
Jonathan pulls Nancy through the portal in the tree, saving her from the creature. Jonathan returns Nancy safely to her room, but she is afraid to be alone and asks Jonathan to stay with her. Steve, dropping by for a visit, sees them together through her bedroom window. Jonathan joins Nancy in her bed, though nothing sexual takes place.The next day they resolve to hunt and kill the monster themselves, purchasing ammunition and bear traps from an army surplus store. Before they head out, Nancy sees a defaced marquee referring to her as a slut. She hunts down and finds Steve and his friends, and as she confronts Steve, Jonathan comes to her aid. Jonathan and Steve get into an argument that escalates into a fistfight when Steve insults Jonathan's family. The cops arrest Jonathan after he inadvertently assaults an officer. Joyce and Hopper decide to investigate together after Hopper discovers his home has been bugged. They track down the woman claiming that a covert facility stole her baby. She is revealed to be El's biological mother, who underwent MK Ultra training while pregnant.
Jane, now 011, was confiscated by Dr. Brenner, with a fake story that Terry miscarried. Mike, Lucas and Dustin are still unable to agree about searching for El. Lucas angrily parts ways with Dustin and Mike again after a failed reconciliation attempt, following the compass alone to the Laboratory while Mike and Dustin search for El in the woods.
Alone in the woods, El misbehaves, stealing frozen waffles (her new favorite food) from a grocery store and shattering the door on an employee. Flashbacks reveal that while on her reconnaissance mission, El accidentally opened the gate between the normal world and the "Upside-Down", allowing the monster through.
While searching for El, Mike and Dustin are ambushed by Troy, threatening Dustin with a knife. He demands that Mike jump off a cliff into the lake where Will's body was discovered, almost certainly fatal. Mike jumps, but is levitated to safety by El, who breaks Troy's arm. Mike and Dustin reconcile with El, and they head back to Mike's house. Lucas sees agents leaving the Laboratory and realizes where they are going: Mike's house to take El.