Flash: Cause and Effect

"Cause and Effect" is the twenty-first episode of season three of the live-action superhero fantasy series The Flash, and the sixty-forth episode of the series overall. It was directed by Nina Lopez-Corrado with a script written by Brooke Roberts and David Kob based on a story treatment by Andrew Kreisberg. It first aired on the WB Network on Tuesday, May 9th, 2017 at 8:00 pm. In this episode, a futuristic criminal refugee from Earth-19 named Abra Kadabra comes to Earth-1 and begins committing crimes. Bounty hunter Gypsy comes trailing after him. Barry takes particular interest in Kadabra as the villain has insight that could be used to save Iris' life. Caitlin Snow suffers a mortal injury and the only way to save her is by reverting her to her Killer Frost identity.