Hopper breaks into the lab while Nancy and Jonathan confront the force that took Will. The boys ask Mr. Clarke how to travel to another dimension.

After Will sees something terrible on trick-or-treat night, Mike wonders whether Eleven's still out there. Nancy wrestles with the truth about Barb.

Nancy and Jonathan swap conspiracy theories with a new ally as Eleven searches for someone from her past. “Bob the Brain” tackles a difficult problem.

Behind the Iron Curtain, a risky rescue mission gets underway. The California crew seeks help from a hacker. Steve takes one for the team.

As Hopper braces to battle a monster, Dustin dissects Vecna's motives — and decodes a message from beyond. El finds strength in a distant memory.