(A/N) Written immediately after 3x18 aired, so it's already been jossed. Oh well.

Cisco perched on Caitlin's desk. She said immediately, "Get your butt off my nice clean desk."

"Excuse you, what are you implying about my butt?" Without waiting for an answer, he scooped up about half the cup's worth of strawberry jello. "So, here's what I don't get about that Pandora's box story."

"The what?" she asked absently, concentrating on her graphs. Woman was crazy for her data, and he was saying that as an engineer, okay.

"You know Pandora's box?" he said through a mouthful of sugary gelatin goodness. "The story about the old-times lady who opened up the box the gods told her not to and - "

"Released all the evils of the world, yes, Cisco, I read Bullfinch's Mythology too. What's your point?"

He knew about Pandora's box from Wishbone, not Bullfinch's Mythology, but he didn't point that out, because her mom hadn't let her watch a talking dog sharing great literature. If there was one thing they'd discussed thoroughly, it was how much Mama Snow had hated joy.

"So, the end of the story? How there was one thing left in the box after war and death and famine and people who cut funding for school lunches had all been released?"

She sat back, looking up at him. "Hope," she said. "That's what was left. Hope."

"Right. What even was hope doing in the box with a bunch of evil things? That never made sense to me. Isn't hope a good thing?"

"Oh, Cisco," she said softly. "Hope is a wicked, wicked thing."

"That's cynical," he said. "Hope keeps you going."

She stood up and touched his face with her fingertips. He lost his breath, which happened sometimes with Caitlin, when he looked at her and his brain went, oh, hey, hi there. Hi, you. Another kind of hope.

"Hope lies," she told him. "It strings you along. Tells you impossible things. Keeps the agony sharp, long after you should have moved on."

"Okay," he said, voice croaking. "Yeah. It's not always good - "

"Hope might be the worst evil of all. Except maybe for me."

Her eyes went blue and her hand on his face went icy cold and -

He woke up screaming.

When his voice gave out, he found himself huddled under his blankets. He'd taken to sleeping under mounds of them, sweating through the night, but it never seemed to thaw the ice that slid through his veins ever since -

"Maybe she's in there," he said.

"She was gone," H.R. told him. "Her heart stopped."

He looked at Julian, who after all had more medical experience than H.R. To be fair, there were washcloths with more medical experience than H.R., but anyway the point stood. "Your brain doesn't die right away when your heart stops, right?" he asked. "It's why you - "

Julian stood abruptly. He looked pale. Positively waxy. "I know what I did."

"Isn't it possible - "

"Killer Frost had taken over completely," he said. His lips were tight and bloodless. "The only way she could do that is if Caitlin were - "

"But - before. You weren't here for it, but we got her back before. She was in there and we got her back, so maybe - "

"She's gone, Cisco," Julian said. He went into Caitlin's lab and slammed the door.

Cisco pressed his face into his pillow.

He and Caitlin had actually had that discussion about hope and Pandora's box and all, sometime after when Ronnie had disappeared into the singularity, before she'd gone to Mercury Labs. At the time, he'd sympathized but privately thought she was speaking out of grief.

Now he knew exactly what she'd meant.

He looked at the CCTV footage and saw Killer Frost, who looked nothing like Caitlin. Different hair, different eyes, definitely different dress sense.

But sometimes she tilted her head or moved her hands in a way that screamed Caitlin, this is Caitlin, and he had to look away.

He had her necklace, entombed in a box that sat on his desk. He hated himself sometimes for not putting it back on her when Julian had ripped it off. He'd stood there clutching it, thinking, This isn't what she wants. But there was a little part of him that was relieved Julian had done it, because maybe - maybe -

But Star Labs had thrown the dice once too often, using Caitlin, using her powers, and they'd paid the price. Caitlin had paid the price. And now Killer Frost was loose.

He dreamed about getting Caitlin back. He dreamed it a lot. He dreamed of Barry talking her out of her icy prison again. He dreamed of Julian kissing her awake, like Sleeping Beauty. He dreamed of going up to her himself, taking her hands and saying her name, and she would blink her eyes brown and throw her arms around him.

He even dreamed of Savitar, doing something totally out of character and taking her powers away like some reverse Santa Claus.

He tried to convince himself that they were vibes, that he was seeing the future, that this would all be fine, but he knew better. The colors weren't the right shade of blue. The edges didn't have the right smear. They weren't vibes, they were just dreams.

Hopes.

Killer Frost went Chaotic Evil through the city, hitting - well, pretty much anything that caught her eye, as far as Star Labs could tell. Cisco got them an advantage when he set special watches on all of Caitlin's favorite stores, particularly the ones that she only allowed herself to purchase from once in awhile - too expensive, Cisco, it's not going to fit in the budget this month.

But when it came to her, that was about the only way he was useful.

"It's not her," Julian, Iris, Joe chanted in his earpiece when he faced her down among the shattered shelves of glittering jewelry, or the wreckage of a particularly high-end shoe store. "It's not Caitlin. It's not."

But she'd spotted his weakness early, and he limped back from every confrontation battered and bruised and more than slightly frostbitten. Julian would wrap up his wrenched knee or clean out the gravel from where he'd skidded half a block, not bothering to scold him for once again trying to get through to Caitlin, through all the layers of Killer Frost -

"She's in there," Cisco said. "I believe it. She's got to be in there."

"She's gone," Julian said harshly, and turned away.

If he had, even once, said You're good to go the way Caitlin used to, Cisco would have either cried or decked him. Maybe Julian knew that, because he didn't.

They avoided each other's eyes a lot these days.

Finally, Barry and Wally sat him down and gently, kindly told him Vibe wasn't allowed to fight her anymore. That if they got a report of her, he needed to go back to Star Labs.

He didn't argue.

They didn't want to hurt her either - she'd been their friend too, even she hadn't been quite what she was to Cisco. Mostly they managed to keep her from living up to the Killer part of her name.

That seemed to be at an end when the police found a severely hypothermic man in the wreckage of his small jewelry store.

Cisco hacked into the records of Mercy General - "does patient privacy mean nothing to you lot," Julian said waspishly, and sighed at the blank faces that turned his way - to check on the patient, dreading to find that he'd died or been permanently damaged by frostbite.

What he found made him yell for everybody. They rushed in, pale, ready for another disaster. But he spun in his chair, vibrating with joy. "The guy had a history of heart attacks, and tests show he'd had another one that evening."

"… yay?" Wally said uncertainly.

"No, no, no - " Cisco leapt to his feet. "Okay, there's this thing, right? This thing, it's called therapeutic hypothermia, when somebody has a heart attack, they chill 'em down - Back me up here," he ordered Julian, who must have learned the technique as a medic. "Isn't that something they do?"

"It is, yes," he admitted reluctantly. "In certain cases, first responders will lower the core temperature, gradually, with cold packs and such, to slow the metabolism and reduce the risk of brain damage after cardiac arrest."

"Which she knew," Cisco burst out. "We talked about it, way back before we even heard the name Killer Frost. What if the guy had a heart attack when she tried to rob his store, and she cooled him down?"

Barry pointed out, "It would be more like Killer Frost to leave him dying on the floor and walk off with most of his inventory. Which, um, she did."

"That's what I'm saying. She didn't have to hit him with the cold whammy. It would just waste her time, with the alarm already going off. Guys, this was Caitlin!"

Julian said quietly, "Cisco, mate, you're grasping."

"She's in there," he said, and watched them shake their heads. "You guys, no, it's a very exact thing, it's not gonna happen by accident - "

Iris gave him a pitying look. He looked away.

"She's in there," he said. "I know it."

Hope is the thing with feathers, perching in his soul. Its beak is razor sharp.

FINIS