Killer Frost is going to be making her presence felt in The Flash sooner than some expected. Season 4 of The CW's speedster show acted very quickly to bring our favorite superhero team back together, but it's also clear that our core characters aren't the same people they were before. In Barry's absence, Wally, Iris, Joe, and Cisco had to find a new dynamic to keep up the fight against dangerous criminals and metahumans.
Once Barry returned, the original Team Flash has been slowly working their way back together, including Earth 2's Harrison Wells. Caitlin was also welcomed back for her desperately-needed scientific skills, and with a promise from her that Killer Frost was gone for good. Viewers quickly learned that Caitlin's evil meta side was merely being suppressed, however - and not always successfully.
While thus far the S.T.A.R. Labs crew seems willing to let bygones be bygones, EW reports that the true test of that will come in episode 5, which airs on November 7. According to actress Danielle Panabaker, one person in particular will be sympathetic to her character's struggle with the dark side:
"When Killer Frost shows up, Iris has a lot of compassion for Killer Frost and a lot of compassion for Caitlin and is pivotal in helping Caitlin reconcile herself with her past and some of the mistakes that Killer Frost made."
According to the synopsis for the episode "Girls Night Out", the mystery of what Caitlin was up to during her absence from Team Flash will be at least partially revealed. And, as is typical of The Flash, Caitlin's dangerous half could appear during Iris' wedding shower.
The Flash writers have seemed intent on giving Iris a much more prominent role on the team in season 4 , which has received some mixed reactions from fans. While adding some depth to a character shouldn't be a bad thing, there has been understandable criticism that her credentials as barista-turned-sometime-journalist don't make for a natural choice as crime-fighting leader in a room that includes a police officer, metahuman superheros, and science/tech geniuses.
As a non-meta, Iris also doesn't seem the obvious choice to advise Caitlin on her situation - although letting her be a thoughtful and compassionate friend is a far more logical arc for her character. The Flash has a tendency to unnaturally breeze past what should be difficult situations, so it's welcome news that the show will explore Caitlin's struggle and quest for forgiveness more thoroughly in upcoming episodes.
The Flash airs Tuesdays at 8pm on The CW.