Will Byers vanishes after encountering a monster while cycling home from a D&D game.  His friends, Dustin, Lucas, and Mike, search for him and find Eleven, a girl with psychokinetic powers, who joins their investigation.  Will's mother, Joyce, experiences supernatural events in their home, believing Will is trying to contact her, while Chief Hopper investigates a nearby suspicious laboratory.  Simultaneously, Nancy, Mike's sister, attends a party, setting another storyline in motion.