Hopper discovers a massive secret: the lab is experimenting with a tear between dimensions, which scientists call "The Gate."
The boys theorize that Will has been taken into another parallel world — something like a shadow version of Hawkins — which they call "The Upside Down."
Joyce and Hopper reunite and attempt to map out clues regarding Will's location.
Nancy and Jonathan team up after she describes the monster. Jonathan realizes the creature matches Will's earlier drawings.