Spoilers for the May 15 episode of The Flash ahead. The clock is ticking, and every second that passes brings Team Flash and the entire world closer to having their brains wiped clean of any knowledge courtesy of the Thinker's Enlightenment, and in The Flash episode "Think Fast," Barry continues to be one step behind. But while the world as they know it may be ending, a new revelation about Killer Frost's origins sends Caitlin reeling. How did Caitlin become a meta on The Flash? It turns out the answer to that question is way more complicated than she thought.
DeVoe is in the final stages of his plan, and Team Flash knows it, but with Wally still off time traveling with the Legends, Killer Frost still stuck somewhere in Caitlin's brain, and Harry losing intelligence, they don't really have many options but to sit and wait for DeVoe to make a move. That move, it turns out, is to use his acquired meta powers of shapeshifting and hacking technology to break into an ARGUS facility and essentially highjack Fallout to use him as a power source to launch his dark matter satellites into orbit. Flash can't stop him and save the ARGUS hostages DeVoe has conveniently staged in the way, so Caitlin and Cisco lobby to be allowed to go in with him. If Barry can bring them into Flashtime (the slow moving reality for Barry when he's really speeding around), they can help save the hostages while Barry goes for the Thinker. With only 12 hours before Enlightenment begins, the team begins training, and that's when things get interesting.
During a practice run, Caitlin is thrown to the ground and has a flashback to when she was little. A young Caitlin is seen riding a bicycle when she falls, her feet getting tangled up in the pedals, keeping her from getting up and out of the street where a truck is driving straight for her. The flashback is short, but it opens up something in Caitlin. Earlier in the day, Caitlin had a session with Team Flash's resident therapist to try to get Killer Frost to re-emerge. The therapist tells her that she's repressing trauma, likely about her dad dying, but Caitlin shoots that idea down. In the flashback, Caitlin's dad is heard running towards her after she falls, but it turns out that the repressed memory isn't about her dad at all. When Cisco vibes her back to her memory so she can see what it is she's been repressing all these years, she sees herself sitting up after her fall, the truck now damaged, a sideview mirror laying discarded on the street. She picks it up and sees her reflection: not a little Caitlin, but a little Killer Frost.
Caitlin wasn't turned into Killer Frost by Savitar (like she thought). Her metahuman genes weren't activated by the particle accelerator explosion or Barry bursting out of the Speed Force, they were already inside her. Assuming her scientist mother didn't experiment on her as a child, Caitlin was born Killer Frost, she was just able to repress it. The idea of Caitlin being born a metahuman opens up many new possibilities in The Flash world. In the immediate future, it raises a lot of questions for Caitlin and her relationship with her mother, who was pretty against Caitlin's metahuman powers to begin with. It also changes everything that Caitlin and the scientists on Team Flash thought metahuman powers were. Was Caitlin's power still caused by Dark Matter? Is she from another universe or another planet? Or is the world just more complicated than Team Flash thought?
Caitlin's Killer Frost origins could also have consequences for Barry and Iris' future children as well as Cecile and Joe's new baby. Throughout the pregnancy, Cecile has developed meta powers of mind reading, and now a kind of mind melding. When Caitlin originally examined her, she said that the fetus did not show signs of meta DNA, and hypothesized that the pregnancy had simply unlocked some residual Dark Matter in Cecile from the particle accelerator explosion. But what if she was wrong? If people can be born metahuman, then maybe Cecile and Joe are about to welcome a little metababy. And maybe, just maybe, the mystery waitress is also one such born meta.
It's unlikely fans will get all the answers before the end of the season. "Think Fast" ends with DeVoe taking over the satellite at STAR Labs and launched Project Enlightenment. For now, Team Flash has bigger fish to fry than trying to uncover Caitlin's mysterious past.