(A/N) I wrote this before the season 4 premiere and it's just taken me this long to port it over to this website.

Iris tore through the curving halls of Star Labs, her shoes squeaking on the smooth floor. She cut through the cortex, her heart beating too fast even for the run, and made for the med lab.

She caught the flash of white hair and stopped dead. Animal fear jittered in her stomach. She swallowed it down and said clearly, "I don't know why I thought they might be kidding."

Caitlin Snow - Killer Frost - straightened up from her computer. "Iris," she said.

"What are you doing here?"

"Working. What does it look like?"

"Those idiots," Iris said, staying well back. She carried a taser now, a nasty little piece of work, and its weight in her pocket was a snarling comfort. "I mean, Julian loves you so of course he wants you back. And Cisco, well, I guess it's habit by now, isn't it? Even after all those times you tried to kill him. But what on earth made you think I'd be okay with this?"

"Nothing," the other woman said. "I don't expect you to be okay with this at all."

Iris didn't know what to call her. On the way back from the cemetery, Barry had filled her in on what she'd said after HR's funeral, and it sounded like so much bullshit to her. If she wasn't Caitlin and she wasn't Killer Frost, then what was she?

"You think you can just come back here and pick up your old life after two months like nothing happened? Like you never helped to kill HR? Like you never would have done the same to me?"

"I know what I did," Frost said. "And I'm sorry. For everything I did, especially to you."

"Is that supposed to make it better?"

"I don't expect anything from you."

"Nothing is exactly what you're getting."

"Yes, you've made that clear." She tapped her pale fingers on the desk. Iris couldn't stop herself from staring at her nails, unpainted and cut short. She remembered when they'd been blue and claw-like, and when mist had drifted off them even at rest.

They weren't misting now. Did that mean something?

"Fuck you," Iris said, and turned to go yell at Cisco until they kicked her out. Preferably to the Arctic Circle, where she couldn't do any more harm than the landscape.

"You were willing to forgive and rehabilitate Savitar," Frost said loudly. Her voice echoed around the med lab. "And he didn't even ask for it. Why am I different? Is it because I don't wear Barry's face?"

It stopped Iris dead. She remembered how easy it had been, to look at Savitar, not-Barry-but-still-Barry, and see the pain underneath the rage and the madness in his well-loved eyes.

"I killed Savitar in the end," she said. And she still woke up in cold sweat sometimes, seeing his dear familiar frame arch backward against the impact of the bullet. Barry, not Barry. "Did you miss that?"

"No," Frost said. "But you gave him a chance first. He was the one who squandered it."

Iris snorted.

"Cisco and Julian might have admitted me back here, by the way. They might even have forgiven me. I don't know. But they don't trust me. There are temperature sensors every five feet in this room. Every ten feet in the rest of the building. They're downstairs working on the rest of the system right now. If the temperature dips by so much as five degrees, then - well, I don't know what'll happen. But Cisco designed it, so it'll be effective."

Iris turned then. "Well, naturally. The protectors of Central City aren't total idiots," she said, although this was news to her. Maybe Cisco had been going to tell her about it, but she'd ended the call and raced over here before he could, ignoring the buzz of her phone in her pocket.

"You don't trust me, you won't forgive me, but you need me, and you know it. That's why you haven't told me to my face to get out."

Iris swallowed.

As if the disappearance of the Flash had been a finger pulled out of a dam, the Central City underworld was spilling over, rising up. Cisco and Wally were doing their best, and their best was very good. They got the occasional helping hand from Cynthia, when she could come over from Earth-19, and backup from Iris and Julian.

But it wasn't enough, and they all knew it.

And Iris might be repulsed in every inch of her skin, looking at the woman who had once been a friend, but she loved her city with every inch of her skin, too - something Cisco would have reminded her of when she went to demand Frost's ousting.

The question wasn't whether Killer Frost could help. Besides the simple consideration of another pair of hands, cold powers could fill in a lot of gaps where speed and vibes didn't cover. The question was whether they could trust her to be there when they needed her.

"Why was it so easy for you to turn?" she said. "Savitar I understood. He'd been marinating in pain and rage for thousands upon thousands of years. But you - all it took was - "

"Dying," Frost said calmly, tapping a few keys on the computer and studying the effect. "I died. And what came back wasn't - wasn't entirely me."

"What did come back?"

Her hands stilled. "I don't really know," she said. "I'd like to think it was something else entirely, but I can't lie to myself like that anymore. I think - that it was the worst of me. The rage. The loss. The grief. The frustration. The helplessness. All the things I'd been locking away because there wasn't time, was there? There's never time to feel any of that. Not in this place."

Iris wanted to spit at her. Wanted to scorn her. Poor widdle Caitlin, were your feelings too much for you?

But she had a point. There wasn't time to feel everything there was to feel. Not at Star Labs, not protecting Central City. You had to pack it away and get on with things. There was no other choice.

Sometimes in the night, in her too-big bed, Iris's own loss and sorrow yawned like a pit of darkness in her belly. She stood on the precipice feeling its hot breath and thought, What if I just let it eat me alive?

"Why were your powers part of that?"

"Something about the cold, I suppose. Or maybe it's because I'd spent a year listening to my mother and my best friend telling me that my powers would consume me, just like all those other things would consume me if I let them. It seemed a reasonable conjunction."

"Oh, did it," Iris said faintly.

"What came back didn't care," Frost said. "And what came back didn't want to care. It was so very freeing. You have no idea. Caring was desperately painful at the best of times, and when it stopped - She didn't want to go back to that. She wanted to surgically excise everything that ever made her care. I suppose it's why I targeted Cisco so often."

"And now you care again," Iris said. "That's heartwarming. It is."

"Believe me or don't," she said coolly. "But I care about Central City. And Star Labs, and Cis - everyone in it. Whether you believe it or not, that includes you."

Iris narrowed her eyes. "And what if you decide that you don't care, again?"

She nodded a little, as if she'd been waiting for this question. She reached out and laid what looked like a tiny remote down on the edge of the desk closest to Iris. "There. That's for you."

"What is it?"

She pointed at a tiny metal circle on the desk in front of her. "It controls this."

"That doesn't answer my question."

"Press the button and find out."

Iris leaned over and stretched out her hand to pick up the remote. Maybe this was a trick, she thought. Maybe this was poison to the touch, or -

She hit the button. Her thumb, slick with sweat, slipped.

Lightning arced out of the device on the desk, leaping to the computer, which let out a high pitched noise. The screen went white and then black. A wisp of smoke leaked out the top and a strong smell of scorched electronics filled the room.

"Oh shit," Iris said involuntarily.

"Hmmm," Frost said. "Did you hit it twice?"

"Uh, yeah. I just fried your computer, in case you didn't notice." Caitlin would have been squeaking like a trodden mouse right now.

Frost shrugged. "Everything is backed up to the cloud."

"What is that?"

"It's for me. I'm going to implant it here." She touched her neck.

"A shock collar?"

"If you like." She tapped her fingers again. There was something nervous in the movement. "Cisco gets all the credit for his gadgets, but everyone seems to forget that I trained as a bioengineer as well. My designs maybe aren't as elegant - " She looked ruefully at the fried computer - "but they'll get the job done. One press was all it would have taken, by the way. Two would - well, you saw."

The fried computer wisped smoke.

"That'll kill you."

"Probably."

Iris dropped the remote. It clattered to the floor. "I can't do that," she said. "I can't hold your life in my hands. I'm not you."

"Is that referring to Caitlin or to Killer Frost?" she asked softly.

Iris had no answer for that.

"Take it or don't," Frost said. "But that's what I'm offering. Not platitudes. Not more apologies. Not reassurances. Those are all just words and we both know it."

Iris leaned down to pick up the remote. It felt far heavier than it had a right to do. She stared at it. "Change the setting," she said abruptly.

"To a no-kill?"

Iris looked up. "Change the setting so I have to do it deliberately," she said. "I refuse to kill you by accident if you're being useful."

Emotion flickered across her pale face. If she'd still been Caitlin, Iris had a feeling she would have recognized it. She took a measured breath. "A one-second lag should do it," she said, making a note to herself.

"You need this back?"

"Just for a moment." She picked up the evil little device and took the remote, moving to another computer out in the cortex. She hooked it up, made some adjustments, and then unplugged it. She handed it back and moved the device to an empty table.

Iris hit the button twice, fast, the way she had before. It sparked, but not like it had before. She hit the button, counted one Mississippi in her head, and hit it again. Electricity arced wildly, starting a small fire on a greasy rag sitting a little too close.

Frost put out her hand and froze it before it could grow into a large fire. It withered and died, smoking feebly.

Iris didn't want to, but she couldn't stop the tremors that wracked her body at the spill of mist, at the wash of cold. Somewhere off in the distance, an alarm started hooting wildly.

A portal opened up and Cisco leapt through it, teeth bared, hands raised. "Hey," he snarled.

"Everything's fine," Frost said, shutting her hands so the mist dissipated. "Just taking care of a fire. You shouldn't leave greasy rags lying around, you know."

Cisco looked at Iris.

"It's fine," she said, forcing her words to stay steady, not to tremble. "All of it." She closed her hand around the remote. "Okay. She stays."

The snarl melted away and he just looked baffled. "That easy?"

"We've discussed terms and conditions," Iris said.

"What does that mean?"

Frost said, "We've come to an understanding, haven't we, Iris?"

"Yes," Iris said, meeting her eyes. "We have."

"Okay," he said, still looking a little baffled.

He watched Frost for a long moment, and Iris turned away from the look on his face. She wondered if this was going to be okay for him, being this close to the person who'd once been his best friend.

"Uh. In that case, I should - I left something - " He gestured vaguely labward.

"Sure," Iris said. "Go on."

He didn't pull open another portal, but walked this time, his shoulders tense as if he was trying not to look back at Frost's eyes following him.

Iris had to look away from that, too.

When he'd disappeared around the bend, Frost said in her steady, calm voice, "I'll let Cisco know when I've implanted it. You can come by and test it."

Iris narrowed her eyes. "Does he know what this is?"

"Of course not," she said. "He would hate it."

"He really would," Iris said, and put the remote in her pocket. "All right. I've just wasted my lunch hour on this, so I should get going long enough to at least grab a sandwich on the way back." She started toward the door.

"Iris."

She didn't want to, but she stopped and looked back over her shoulder.

"I'm sorry about Barry," she said.

Light from the windows caught her eyes. They were brown. Caitlin's eyes. It also glinted on the ice-white of her hair.

"We're getting him back," Iris said. "We are. I have the date saved."

"I know," the other woman said, and went back to her lab.

As Iris walked out of the cortex, the weight of a life rode in her pocket.

It felt unsettlingly good.

FINIS