On his way home from a friend's house, young Will sees something terrifying. Nearby, a sinister secret lurks in the depths of a government lab.

Lucas, Mike and Dustin try to talk to the girl they found in the woods. Hopper questions an anxious Joyce about an unsettling phone call.

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.

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.

Dr. Brenner holds Hopper and Joyce for questioning while the boys wait with Eleven in the gym. Back at Will's, Nancy and Jonathan prepare for battle.

As the town preps for Halloween, a high-scoring rival shakes things up at the arcade, and a skeptical Hopper inspects a field of rotting pumpkins.

Dustin adopts a strange new pet, and Eleven grows increasingly impatient. A well-meaning Bob urges Will to stand up to his fears.

Nancy and Jonathan follow a lead, Steve and Robin sign on to a secret mission, and Max and Eleven go shopping. A rattled Billy has troubling visions.