"Killer Frost" continues a long-running tradition on The Flash: It lets an evil speedster treats Barry like his personal ragdoll. Savitar is so fast that, even to Barry, it seems like he's racing across the city instantaneously. But neither Savitar nor his equally gravely voice lackey, Doctor Alchemy, prove to not be Barry's most pressing problem. Wally is still trapped in that weird cocoon. Caitlin is on the fast track to becoming Killer Frost, after using her powers to save Barry from being stomped out of existence. Perhaps most importantly, Barry finally has to face his past mistakes — namely, time traveling and creating Flashpoint — and how those choices wrecked the lives of the people he loves.
Barry: "Let me help you."
Caitlin: "Like you helped your mother or Wally or me? You keep messing with everyone's lives, wrecking everything and we're left behind picking up the pieces of your mistakes."
Sure, Caitlin makes this harsh statement after she kidnaps Julian in order to get him to help track down Alchemy. But did she lie? Not at all. She doesn't stop there: She also doesn't hesitate to let Cisco know Dante was alive until Flashpoint, leaving his friendship with Barry on uneasy ground once again. I'm still not on board with this frankly nonsensical idea that using powers somehow turns a person evil, but her journey into Killer Frost does makes Caitlin a far more interesting character. Gone are those terrible storylines that revolve around her love life. Danielle Panabaker even seems to step up her game as an actress when she's playing it evil — which means that Killer Frost's sass is a nice addition whether Caitlin goes full rogue or not.
In her quest to get Alchemy to help remove her metahuman abilities, Caitlin does one heinous act after another. She lies to Joe to interrogate one of Alchemy's captured underlings. She stabs Barry so he won't follow her. She threatens Julian's life and that of one of Alchemy's followers so she's able to track Alchemy down. But in many ways, it's evident The Flash sorely needed Killer Frost. This is easily the most fascinating storyline of the season. So often, superhero stories depend on a black-and-white moral code — especially on a network like the CW, in which complexity isn't always a priority. (Just look at Arrow.) Caitlin's arc brings up a lot of interesting questions about the nature of heroism, the choices superheroes make, and the devastating consequences of those choices.
After a showdown between Cisco and Caitlin — which Barry crashes despite his leg not being fully healed — she finds herself in the pipeline of S.T.A.R. Labs. Even Barry's tried-and-true pep talks don't help. "For a hero, Flash, you sure let a lot of people around you die," she says after he tries to appeal to her. When Joe cuts Wally out of the cocoon, Barry realizes they need Caitlin now more than ever. Wally has the speedster powers he's longed for, but he doesn't seem like himself. It's as if his mind is operating at an entirely new speed. So, Barry makes a bold gambit. He lets Caitlin out, but gives her an ultimatum: She has to kill him if she wants to get out of the room. "You want to be the villain, this is what they do," he says.
Of course, Caitlin can't do it. As angry as she is about her predicament and Barry's mistakes, the good person underneath Killer Frost's icy veneer still exists. So, she puts her skills as a biochemist to good use, finds a way to get Wally's mind and body working at the same speed, and saves the day. Basically, she proves she can be just as good a hero as Barry. Can The Flash find a way for her to keep her powers without becoming a bloodthirsty villain? Even though Caitlin turns things around by the end, there is still the lingering question of how exactly Team Flash will help her. Also, she left quite a mess in the wake of her short-lived villainy: Julian remembers she kidnapped him and wants to turn her into the police.
Barry goes to talk to Julian at the hospital and he agrees to keep Caitlin's identity as Killer Frost a secret under one condition: Barry must quit his job as a CSI at the police department. "Your moral compass is broken," Julian tells him. Barry reluctantly agrees, demonstrating how much he cares for his friends. But what is he going to do next? I'm guess when original flavor Harrison Wells died, he left Barry his fortune along with S.T.A.R. Labs. But still. Seriously, Julian? I had the same reaction as Iris when she heard the news: "That son of a bitch!" At this point, Julian has yet to prove himself to be a character worthy of any attention. His jealousy and animosity toward Barry has little grounding in reality. The reveal at the end that he's Doctor Alchemy — which may be a red herring considering how early it is in the season — isn't enough to make him worth all the screentime he takes away from characters who have been on the show since day one but have yet to get much development.
That brings me to an important point: I would love to give this episode a full five stars. The action is amazing, thanks to the emotional weight that's behind each sequence. Kevin Smith is obviously a director suited for the series, as we learned with last season's "The Runaway Dinosaur." We're finally getting Wally as Kid Flash, even though he owes his powers to this season's Big Bad. Caitlin finally feels complex. And yet, The Flash still seems incapable of giving more than one female character an actual storyline at a time. When we learned Iris would get more to do this season, I didn't think that meant just being Barry's girlfriend and personal therapist. As great as "Killer Frost" is, I can't ignore how The Flash continues to sideline one of its best and most important characters. At this point, it isn't an oversight. It's a telling flaw that holds the series back from greatness that remains just out of its reach.