Chapter Seven: The Lost Sister

"Chapter Seven: The Lost Sister" is the seventh episode of the second season of the American science fiction horror drama television series Stranger Things. Written by Justin Doble and directed by Rebecca Thomas, it was originally released on Netflix in the United States on October 27, 2017, along with the rest of the second season.

Created by the twin Duffer Brothers, the series, set in the 1980s, follows the fictional town of Hawkins, Indiana, and the supernatural happenings that occur within it. In "The Lost Sister", Eleven (Millie Bobby Brown) discovers from her comatose mother that there is another girl who, like her, was taken by Dr. Martin Brenner (Matthew Modine) to be given supernatural powers. Eleven meets the girl, Kali (Linnea Berthelsen), in Chicago, along with her group of punk friends, who help Kali get revenge on the people that assisted Dr. Brenner in his experiments.

The episode was written both out of the Duffers' admiration for Brown's acting in the first season, and for them wanting to further explore Eleven's childhood in a way that would ultimately benefit her arc in the season. With a different tone than the rest of the series at that point, the idea of it being the second half of the season finale instead of a standalone episode was brainstormed, but ultimately decided against. The look for Kali and Eleven were both heavily scrutinized; Brown enjoyed her new outfit for the episode, which was partially based on Madonna's style. Upon release, the episode received generally mixed reviews from critics, with most agreeing that it was the worst episode of both the season, and the series up to that point, particularly for disrupting the flow of the narrative. Despite the mixed reception, Kali was eventually brought back for the fifth and final season.