After the creepiest post-Halloween episode ever last week, The Flash chills out this week, literally, with “The Icicle Cometh.” It winds up being yet another really dark episode that finally reveals Killer Frost’s traumatic origins — and the episode returns the icy queen to the show.

Spoilers follow for The Flash Season 5, Episode 6: “The Icicle Cometh.”

“The Icicle Cometh” aired Tuesday night, and it introduced us to Caitlin’s father who, true to the build-up in recent weeks, has been alive this whole time. We’ve known for awhile that The Flash had cast actor Kyle Secor as Thomas Snow. He was first teased towards the end of Season 4, and after five episodes there’s finally a genuinely good payoff.

Thomas Snow had ALS and used experimental cryogenic gene therapy on himself to half the disease, but it also essentially gave himself ice cancer. Because she had the same genetic market for ALS, Thomas used a similar, but safer (maybe?), version of the treatment on Caitlin when she was just a kid. Split personalities is a side effect of the process, and Thomas has his own evil alternate personality.

'The Flash' Thomas Snow
Thomas Snow has an icy secret that we all should've seen coming.

Thomas named Caitlin’s alternate personality Khione, the Greek goddess of snow, which we learned about in “All Doll’d Up,” so he’s comically surprised to hear the crude “Killer Frost” name they’d given her.

Things come to a head when they all realize that Thomas’ version of Killer Frost, dubbed “Icicle” has been in control the whole time, and he wants Caitlin’s help to “cure” away his good side. He almost gets away with it, and the only way they’re able to defeat him is when Caitlin breaks down the mental barrier in her head to reveal that Killer Frost was still in there all along.

As it turns out, the power that DeVoe used on Caitlin in Season 4 didn’t remove her meta-human DNA. He actually used Brainstorm’s powers to put a mental block on her, which means that Team Flash can science a way to bridge the gap once again.

It’s exciting to see Killer Frost’s return, even in this limited capacity, but it feels so bittersweet to know that her maniacal father experimented on her with controversial gene therapy and that’s the reason why she’s had to deal with this.

This also raises another question after all these years: Killer Frost only emerged after Flashpoint, so is all of this still Barry’s fault? The Flash may never answer that questions.

The Flash airs Tuesday nights on The CW at 8 p.m. Eastern.

Watch the totally awesome Batwoman teaser for this year’s Arrowverse crossover, called “Elseworlds.”

Batwoman does almost nothing in her first teaser trailer and she still looks impossibly badass.
Photos via The CW