S3E5 · Chapter Five: The Flayed

Complete story — includes the ending

Hopper and Joyce search one of the abandoned properties, discovering a hidden laboratory. Grigori arrives to kill them, and they narrowly escape with a hostage–a Russian scientist named Alexei–in tow. Dustin, Steve, Robin, and Erica arrive in a Russian lab underneath Starcourt and hide from Russian soldiers unloading crates from the elevator. Attempting to find a communications room, the group discover a large testing area where scientists try to force open a portal to the Upside Down. As Alexei does not speak English, Hopper and Joyce take him to Murray–the only Russian speaker they know–to translate. Grigori tries to follow them but loses the trail. Nancy and Jonathan regroup with Eleven, Mike, Lucas, Max, and Will and then theorize that Billy and Driscoll are both possessed by the Mind Flayer, who uses them to "flay" (possess) people to create an army. The group decides to visit Mrs. Driscoll at the hospital to learn more but discovers she is missing. They are attacked by Tom and Bruce, who are now part of the Flayed and dissolve into a single organic mass resembling the Mind Flayer after Nancy and Jonathan kill them.