It's a strange day at the office for Team Flash when Barry loses all of his memories in an attempt to defeat Savitar, and Killer Frost shows up to help. In "Cause and Effect," Cisco and Julian try to prevent Barry from making new memories in an effort to throw off Savitar, but mistakenly erase Barry's memories instead. Barry's lack of memories also erases Savitar's and takes away Wally's speed (it's complicated), leaving Killer Frost as the only one who can come in and save the day. Killer Frost helps Barry on The Flash, but Caitlin isn't back to normal yet, and she might never be.
Killer Frost tells Team Flash that her motive for returning to STAR Labs was to help Savitar get his memories back, helping Barry and Wally was just the price of that. But, as she worked with Cisco and Julian, Cisco is able to tease out small bits of the Caitlin he knows and loves, proving that she's still in there. And, in the end, she does save Barry, just like the old days, sparking some hope in Cisco, Julian, and Barry. Unfortunately, when they offer to let Killer Frost stay with them at STAR Labs, she refuses. Even when Julian declares he loves her and promises that he'll find a cure, Killer Frost turns around and leaves. However, it does look like there might be hope for Caitlin yet.
When Killer Frost gets in the elevator after Julian's declaration of love, for a moment her icy blue eyes turn back to their normal color. Caitlin can be saved, Killer Frost just has to be willing to let go before she crosses too far into the dark side. Hopefully, Julian won't be too heartbroken to keep working on a cure for Killer Frost, because I think I speak for everyone when I say we could really use Caitlin Snow right about now.