Nocturnal Me
performed by Echo & The Bunnymen

Will's father Lonnie assures Joyce that her experiences are hallucinations. The boys conclude that Will is trapped in an alternative dimension which El calls the Upside-Down. After Will's funeral, the boys ask Mr. Clarke about dimensions, who he tells them that a spacetime tear could create a passage between dimensions. The deputies inform Hopper that Barb's car was found by the state; Hopper finds the state's involvement suspicious. Positing that an tear in spacetime would disrupt the electromagnetic field, the boys follow their compasses to find the source of the disruption. El remembers being placed in a sensory-deprivation tank to telekinetically intercept information from a Russian spy; while listening to the spy, she came across the creature. Scared of finding the gate, El directs the compasses away from the laboratory. Lucas notices the distortion and confronts her. Mike defends her, and he and Lucas fight. El telekinetically flings Lucas off Mike; Lucas recovers and runs away. In the woods, Nancy and Jonathan find a wounded deer, which the creature drags away. Following the blood trail, Nancy crawls through a passage to the Upside-Down world and discovers the creature feasting upon the deer.