Neither Caitlin nor Frost (formerly known as Killer Frost) had much of a part to play, but the promo for the next episode combined with the episode description proves that Caitlin will be the one needed for Team Flash to stand a chance against a certain returning bad guy: Grodd.
The Flash delved into some comic lore with “A Girl Named Sue” to finally introduce none other than Sue Dearbon, while the real Iris struggled to find a way out of the Mirror World to reunite with her husband and reveal the imposter.