When Mon-El and Hank bring Kara to Earth-1 to ask Team Flash for help, Music Meister puts Barry under his spell as well and traps him and Kara in a musical where they have to finish the story to escape... and if they die in the musical then they die in real life as well. This story line started at the end of Supergirl: "Star-Crossed", Season 2, Episode 16.

Barry travels to 2024 to discover who Savitar is and use the information to save Iris. However, he soon discovers that Team Flash was destroyed when Iris was killed... and Barry is responsible. Meanwhile, Killer Frost finds someone who can give her what she wants.