Finding Strength, Finding Home

Billy survives at the end of season 3, but he is stuck as a ghost until El can reconnect him to his body. He gets to follow El around and see how she adapts to her new home and her new life. When El finally gets her powers back she discovers that Pappa is not done with her and has been building an army. El goes back to Hawkins to get Hopper back and to stop Pappa once and for all.