Barry and Kara returned to STAR Labs with their latest conquered foe- a teleporting metahuman named Shawna Baez, christened Peekaboo by Caitlin- in tow, both of them flushed with victory. No sooner had they placed Peekaboo in her cell in the pipeline, however, than they realized that something was wrong. It was quiet- too quiet. A deep, tomblike silence hung over everything, like the calm before the storm. A quick search of the building revealed that Hartley's cell in the pipeline was empty and Cisco was gone, neither in the Cortex where they had left him nor anywhere else in the building. Barry exchanged a troubled look with Kara, both of them coming to the realization, in the exact same moment, that something must have happened involving those two.

"You said you knew what happened to Ronnie and how he was still alive," Cisco said in the security footage from the pipeline they were watching on a monitor in the Cortex a few minutes later. "And you said Professor Stein was at STAR Labs the night of the explosion."

"Yes," Hartley replied.

"Why?" Cisco asked.

"The mystery isn't why Stein went to STAR Labs that night," Hartley said, in the smug mocking tone that was quickly becoming familiar to Barry. "It's why he didn't leave."

"Tell me," Cisco said, in as close to a demanding tone as he could manage- he wasn't particularly intimidating.

"Can't," Hartley replied, still in that mocking tone. "Have to show you."

"You are not getting out of this cell," Cisco insisted.

"Fair enough, but I know you, Cisco," Hartley replied, sounding unconvinced. "I know how much you looked up to Ronnie. He was like family, a family you built yourself here. I know how much you want to see that family healed. Let me help you."

"I don't believe you," Cisco said, almost angrily, as if he were wondering how Hartley could dare use his emotions against him to taunt him this way.

"Well, I'm telling you the truth, Cisco," Hartley replied. "When you're ready, you know where to find me." After that, Ciso walked out of frame, and Hartley retreated to one corner of his cell to sit in contemplative silence. Barry exchanged another grim look with his sister. That would seem to have been the end of it, but Hartley's empty cell and Cisco's absence would also seem to suggest otherwise. Chewing worriedly on his bottom lip, Barry reached for the nearest keyboard and hit a key on it a few times to advance the security footage forward, one frame at a time. He stopped and let it play when Cisco reentered the frame. He slipped a pair of power dampening cuffs through the slot that Hartley was given his meals through and waited for Hartley to take him.

"I didn't know you enjoyed yourself a bit of rough play," he said with a teasing smirk as he put the cuffs on.

"If I'm gonna let you out, I'm not taking any chances," Cisco replied.

"Curiousity's a maddening thing, is it not?" Hartley asked. Cisco didn't answer, or perhaps he was deliberately ignoring him, keeping his attention on opening the door of his cell. A minute later, they were gone, disappearing from the pipeline and the camera's view.

"Do we have any footage of the outside of the building?" Kara asked, her voice tinged with panic.

"Hang on, let me check," Barry replied. He clicked through the different camera feeds until he found one that showed the outside of STAR Labs. Hartley and Cisco appeared in it, roamed around for a bit, discussing something between themselves- soundlessly, since this particular feed didn't have audio- then they turned and disappeared up the nearby stairs and out of the frame.

"What the hell was Cisco thinking, letting Hartley out?" Kara demanded once Barry had switched off the monitor.

"You heard," Barry pointed out, thinking that in this case, Cisco deserved at least a modicum of sympathy. "Hartley told him that he knew what happened to Ronnie. That he knew how to find him."

"But we don't know if that's even true," Kara said frustratedly.

"Obviously Hartley was very convincing," Barry replied dryly. "If there's anything we know about him, it's that he's very good at getting inside of people's heads."

"Unfortunately," Kara growled.

"Look," Barry said. "Obviously we're not going to be able to find out anything more from here, so I'm going to head to my lab and start looking for Hartley and Cisco from there. Sound good?" Kara nodded, and off Barry went.

He found Cisco much sooner than he expected to- he was lying unconscious on the floor of his lab when he entered it.

"Cisco!" he cried, running over to him and attempting to shake him awake.

"What happened?" he asked when he finally stirred, wincing and groaning in pain as he did so.

"Hartley," Cisco explained. "I let him out and he brought us here, and then he got the drop on me. He used his cochlear implants to put me down, and then he escaped."

"Well, did he at least actually tell you what happened to Ronnie?" Barry asked. When Cisco shot him a puzzled look, he explained, "Kara and I saw the security footage from the pipeline."

"Oh," Cisco said quietly.

"You haven't answered my question," Barry pointed out after a few minutes of silence. Cisco nodded.

"He did," he said. There was a pause, presumably while he gathered his thoughts, then he went on, "Professor Martin Stein was at STAR Labs the night of the particle accelerator explosion. He specialized in transmutation, molecular transmogrophy, quantum splicing-"

"Taking two things and making them one," Barry interjected.

"Exactly," Cisco said, nodding. "Anyway, the accelerator explosion somehow transformed Ronnie into, essentially, pure energy, and then the dark matter merged him with Professor Stein."

"So the reason that Ronnie hasn't seemed like himself lately-" Barry began.

"Is because he's not," Cisco finished for him. "He's Martin Stein, in Ronnie's body." There was a long silence, then he said, "I shouldn't have let Hartley out. I should have known that it wasn't worth the risk."

"I don't know that it wasn't," Barry replied. "And anyway, it doesn't matter now. We have a much more pressing matter to deal with."

"Right," Cisco agreed, though he looked relieved to not have been taken to the proverbial woodshed for setting Hartley free. "We have to find Martin Stein."