Caitlin's brain kicked into autopilot, blocking out the panic to do everything that needed to be done. Oliver didn't answer his phone, and neither did Barry, so she punched in Felicity's number while she watched Harry drag his hands through his hair. She explained to Felicity that Oliver and Barry were in danger and Felicity said she'd check on them. Then she called Wally, who flashed over to the lab and then flashed her and Harry to Star City, and then zipped back to Central to hold up the fort. When they arrived in the Arrowcave, the panic only intensified.

"Oh, no," she breathed when she saw Barry on the cot, eyes closed.

"He's just sleeping," Oliver said behind her in a low voice. "He was unconscious for a while, though."

She stared at Barry's limp figure. Felicity stood at a distance, watching pensively, and Harry was bent over with his head pressed into his hands. "Cisco," she said to Oliver. "He hurt you?"

Oliver nodded, expression unchanging. "He hurt Barry worse, though. He seemed a lot angrier. What happened to him?"

Harry's head snapped up. "What happened, Queen, was you antagonized him and pushed him off of the deep end!"

"Harry," Caitlin snapped. "This would have happened anyway. There's no need to assign blame."

Harry's face told her that he thought there was every reason to assign blame, but he kept quiet and started pacing instead. Caitlin turned to Felicity. "We need to find Cisco now, before he hurts anyone else."

"I'm on it," Felicity said automatically, and started typing furiously at her keyboard. A couple minutes later, she said, "He's not on any of the city's security cams. If he's in Star City, we don't have eyes on him."

Of course they didn't. Of course this had to be as damn hard as it possibly could. "We'll have to go back to Central City, then. I'll call Wally. Do you mind if we leave Barry here until he wakes up?"

She barely finished the sentence when Barry let out a low moan and rolled over. She rushed to his side and he blinked at her. "Caitlin," he said blearily, and then his eyes widened with panic. "Cisco- where is he?"

"We're going to find out," she said in the calmest voice she could muster. This only seemed to make Barry worry more, because he sat up quickly.

"This is all my fault. I shouldn't have brought him here, I shouldn't have fought him, I shouldn't have pushed him." He tore his hands through his hair. "I should have-" He broke off, and his eyes were dull with guilt. "This is all my fault."

He's right, it is, a cold, mean part of her brain said. This is because of Cisco's grief, which is all because of Barry. "No, it's not," she said firmly.

"But it is," he said softly. "I should have seen that he was struggling so badly." His eyes were shining and she knew he was beating himself up. Caitlin wished that she could tell him not to, but the cold, mean part of her brain was right. Barry caused this, in part. But so had she. She had been so busy worrying about her powers and her problems that she hadn't realized just how bad things were getting with Cisco. Sure, she had spent every moment at his side for the last three days, but it had started long before that. "I should have been a better friend."

"Me, too," Caitlin agreed. "But that doesn't do us any good right now. What we need to do right now is find Cisco. Can we do that?"

Something about her choice of words made a muscle in his face twitch. He stood up, face set with resolve. "Yeah. Let's find Cisco."

I can see everything from in here.

Every world, every timeline, every possibility.

I see a world where STAR Labs is thriving. I see a world where Caitlin is happy and safe. I see a world where my brother is alive. They are drastically different from the world that I know, but there's one common denominator that ties them together-

Barry Allen is gone.

Arrogant, headstrong, reckless Barry Allen, who races through time and alters history at his whim. He'll change the past for himself- to be faster, to get his mom back, but he won't do it for me.

I guess I shouldn't have expected him to. I'm an engineer, we're kind of the "do-it-yourself" type.

And if you want something done right, you don't wait for Barry Allen to do it for you. You have to do it yourself.

Now it's all too clear to me what needs to be done. What I should have done a long time ago.

Caitlin stood in Cisco's workshop, taking in the horror she should have noticed sooner. On his desk lay a mess of diagrams and pictures, some hand-drawn and others computer-rendered. Pictures of lungs and brains and hearts. Depicting and calculating the vibrations of the human body. A notebook, pressed open with a paperweight, was covered in messy equations and numbers. Phrases like "beats per minute" and "breaking point" and "total failure" jumped out to her, and the room spun. She pressed her hands against the desk to keep herself upright.

"You're telling me none of you noticed this?" Harry asked incredulously. "Is that how much you've been neglecting him, that you don't notice painfully obvious red flags like this?"

Caitlin didn't respond to that, because there was nothing she could say, because she knew it was true. At least in part. Instead, she said, "He's been losing time. That could explain-" She broke off, and felt a wave of guilt. Barry was right. If they'd paid better attention to Cisco, maybe things wouldn't have exploded like this, but they'd all been so focused on their own problems and motives that they had forgotten their friends.

Namely, a friend. The friend who held everybody else up, who held the team together, who was strong so that no-one else had to be. Strong until he wasn't, until he couldn't be anymore.

"What does it mean?" Barry asked in a hoarse voice.

"You said when he blasted you down, it was more powerful than anything you've ever seen him do." Barry nodded. "He must have… he's been learning how to use his powers to… to hurt people." Her throat went dry. "To really hurt people. That's what he's been doing, that's why he's been blacking out and forgetting things…" It all seemed so remarkably clear now, but that provided no comfort. All she felt was angry at herself for not noticing, for failing him.

Harry picked up Cisco's notebook and paged through it, brow knitted with tension. His fingers paused on one page and he stopped dead. "You'd better look at this, Snow," he said in a low voice. He handed the notebook to her and she forced her reeling brain to concentrate.

1 billion beats per minute and then a complicated equation about mass and force, but it was all too clear to her what it meant. After all, she only knew one person whose heart beat at 1 billion beats per minute.

"He's going to kill you," she said in a hollow voice, and turned to face Barry.

Barry's face drained and he shook his head. "He wouldn't."

Caitlin pressed her hands against her forehead. "He wouldn't. But Reverb would." As soon as she spoke, Cisco's words from the last three days echoed in her head.

I wanted to kill him. I enjoyed it.

I didn't know I could hate that much.

Me either.

He screwed up our lives out of pure selfishness. He killed my brother.

"He wants to make you pay," she said, realizing. "You- you hurt him so badly. You're the reason for all of his grief." There was no accusation in her voice, she was just talking through it, but Barry still looked like she'd kicked him in the gut. "He wants to hurt you."

"He wouldn't," Barry repeated, shaking his head. "Cisco couldn't do that. He's not Reverb. He couldn't do that."

"Maybe not," a loud, harsh voice drawled, and Caitlin's blood froze in her veins. "But I am Vibe, and trust me, I can do that. And I will."