Warning! The following contains spoilers for The Flash episode "What's Past Is Prologue". Read at your own risk!
Team Flash went through hell and back to devise a strategy to defeat Cicada, and it almost ended up being all for naught until other factor came in play that could be the key to defeating the Season 5 villain. Apparently, Caitlin and Killer Frost are immune to Cicada's dagger's powers and could end up being the game-changing factor in what will bring about his defeat.
Things kicked off when Nora worked out a grand adventure through the show's past to construct a device capable of defeating Cicada's dagger. If all went according to plan, Team Flash could "time hack" and hide the device so that they could access it in the future. It was a bold gambit, but the best idea the team believed they had at stopping Cicada. The dates were laid out, and Barry and Nora went to make the plan work.
Of course, things didn't go as smoothly as the duo hoped, but Barry and Nora eventually made their way back and went off with Ralph and Cisco to confront Cicada at the hospital. Things seemed to be swinging Team Flash's direction, especially after Cisco was able to vibe the dagger into space. Unfortunately Cicada was still able to pull the dagger back and ended up sapping Team Flash of their powers.
Things took a sharp turn after that, and everyone was on the ropes as Cicada had the clear advantage over everyone. The villain had the speedster right where he wanted him, but before he could strike a killing blow, he was slammed against a van by a cool blast. The forceful wind came from none other than Killer Frost, who is apparently immune to the effects of Cicada's dagger.
CinemaBlend's Deputy TV Editor Laura Hurley spoke to actor Chris Klein during the red carpet event for the 100th episode about the big reveal, and he explained how big the moment is for Team Flash, as well as for Danielle Panabaker's character.
A big arc for Caitlin and Killer Frost? It sounds like The Flash team listened when Twitter sounded off after Caitlin lost her powers last season. Caitlin will now play a meaningful role in the defeat of Cicada, although Chris Klein teased it won't be as simple as freezing him and calling it a day. Perhaps that trip to the past will end up doing more harm than good after all.