S4E7 · Chapter Seven: The Massacre at Hawkins Lab

Complete story — includes the ending

Joyce, Murray, and Yuri enter Kamchatka and witness Hopper and his fellow inmates fighting the Demogorgon. Hopper stops the creature with a flaming spear while Murray and Joyce subdue the guards and open the prison gates, allowing Hopper and Antonov to escape. Joyce and Hopper are reunited. Dustin, Lucas, and Erica theorize that Vecna has created a portal at the site of each murder, which they communicate to the older teens in the Upside Down. Both groups meet inside Eddie's trailer at the gate where Chrissy died. Robin and Eddie emerge unharmed, but Vecna possesses Nancy. She discovers that he is Victor Creel's son, Henry, who killed his mother and sister with his psychokinetic powers before falling into a coma and being placed in Brenner's care. Henry became Subject 001 in Brenner's attempts to replicate his powers and later the orderly whom Eleven befriended. Eleven finally remembers that Henry committed the lab massacre and tried to kill her when she refused to help fulfill his murderous ambitions; Eleven overpowered Henry and sent him to the Upside Down where he eventually became Vecna.