S1E5 · Chapter Five: The Flea and the Acrobat

Hopper searches the lab before being knocked out by the lab's guards. The boys ask their science teacher, Mr. Clarke, if it would be possible to travel between alternate dimensions, to which he answers that there could be a theoretical "gate" between dimensions. Hopper awakens at his house and finds a hidden microphone, realizing that Joyce was right the whole time. The boys follow their compasses, searching for a gate that could disrupt the Earth's electromagnetic field. Eleven recalls memories of being placed in a sensory-deprivation tank to telepathically eavesdrop on a Soviet man speaking Russian; while listening, she accidentally came across the Demogorgon.

Fearing another encounter with the Demogorgon, Eleven redirects the compasses. Lucas misinterprets this as an act of betrayal, leading Mike and Lucas to fight and Eleven to telekinetically fling Lucas away from Mike. While Dustin and Mike tend to the unconscious Lucas, Eleven runs off. Nancy and Jonathan formulate a plan to kill the Demogorgon. While searching in the woods, they come across a small gate to the Upside Down. Nancy crawls through it but inadvertently draws the Demogorgon's attention. Jonathan unsuccessfully tries to look for Nancy, as the gate to the Upside Down begins to close.