Oh my God! I never thought this would take a lot of research. Hahaha! I've tried to keep the science as plausible as possible. I hope it pays off. Anyway, you know the drill, so I'll leave you to it! Happy Reading! XOXO

Chapter 4

"A ghost ghost?" Felicity asked Joe as Cisco cued up the drive. They all gathered around the engineer at the room's main computer station. Even Digg, who had come out from Barry's treatment room to greet the detective, found himself wandering over.

"See for yourself. We've tried to put together Barry's timeline…"

"Wait, I thought your captain took you off the case," Caitlin interrupted.

"…Captain Singh didn't want me to take the lead but he allowed me to work on the sidelines. That drive has everything we've got so far." Joe paused as he let Cisco work the computer. He took a deep breath and faced Caitlin again but his eyes were clearly on the treatment room, "How is he?"

"Still touch and go," Caitlin sighed. She saw Joe falter before he struggled to school himself. That more than anything told her that she had to emphasize the positive, "But his vitals are holding. Have you heard from the hospital yet?"

"They've sent the results on the drive over. I haven't had a chance to look at them yet," Joe said as he remembered the email he had gotten not 10 minutes ago. He took out his phone and tapped in a few commands. "I've sent them over to you."

"Thanks," Caitlin said as she approached the other computer terminal. But before she could open the results, Cisco had launched a collage of all the video files the CCPD had pulled from their own network onto his screen.

"Okay, here's everything… which, apparently, is a whole lot of nothing," Cisco remarked as the various feeds started to cut to white noise.

"Barry clocked in at 8:15 a.m., booted up his computer, arranged a few files, tidied up his workspace, and did some data entry until 8:25 a.m. He received a short phone call then went out of the precinct at around 8:30 a.m. Then this," Joe said as he pointed out to the irregular waves of white dots amidst the gray background of the screen. "I.T. says there was a glitch in the network. Barry comes back ten minutes later with a slushie, goes back to his office, works on his computer before Caitlin found him," Joe narrated, trying to keep his voice level as his brain dredged up the fact that if not for the doctor's timely intervention, his son could have very well died.

"That glitch could open the possibility for a security breach," Felicity said, trying to refocus the detective to the task at hand.

"And the feeds could have been scrubbed," Oliver noted.

"Our techs looked," Joe said, "But they haven't found any. The firewall's intact. They haven't found any viruses or malware. There were no data dumps or any signs of illegal access."

"This is all the video you have?" Felicity pressed.

"This is all we have from the CCPD and the cameras from up and down the street. Look, we just have a skeletal I.T. crew and they double as our digital forensics division. They're a little backed up right now, trying to clean up video from feeds that weren't affected by the glitch."

"Wait, was the whole block affected or was it just CCPD?" Felicity asked. There was just something that didn't sit right with her. She knew that the Central City grid was networked wirelessly, so it mattered if this glitch was an isolated incident or not.

"Half the block was affected. We were able to get feeds from across the street but they're more than just a little bit grainy. That's why our techs are having such a hard time."

"And all these cameras record audio and video, right?"

The detective nodded.

Felicity was on a roll. "May I?" She asked Cisco, as she gestured toward his seat.

"Go ahead," the engineer said as he stood to the side and allowed her to commandeer the workstation.

"What are you thinking?" Oliver asked Felicity as her fingers flew over the wireless keyboard.

"I just want to check something," she said as she cued up the digital signal processing software she had gifted Team Flash many months ago. She fed the CCTV files to it, applied the necessary filters and waited for the read-out on her screen. "See, here," she said as she pointed to the display just as the video cut to white noise," Look."

"What are we looking at?" Digg asked.

"The waves on this depict signal characteristics – amplitude, frequency, jitter and the like. If the data was scrubbed or erased, you would expect a flat line that signifies no signal or no data. But here," she said as she pointed at the multitude of wriggly waves that crazily exploded onscreen, "you…"

"See a lot of noise," Cisco stated, "which means that the data wasn't scrubbed."

"Uh-huh, the signal was jammed," Felicity concluded. "It makes something look a lot like nothing," she said as she allowed the video files to continue playing out.

"Couldn't that have been interference from peoples' phones?" Caitlin asked.

"Not if it affects all the cameras in half a city block," Oliver surmised.

"Could be our perp's window of opportunity right there," Joe said as he contemplated the latest development.

"Did you get any feeds from analog cameras? Or at least from cameras that transmit their data through a wired network?" Felicity asked the detective. "Maybe we could get more information from those."

"That's the thing. There are a few. And this is where it gets more interesting," Joe said as he pointed at the files that held the said videos.

They watched the screens as Felicity cued up the feeds.

"See!" Joe said when the videos began to track Barry as he went out of the precinct.

"So the cameras were out of focus," Diggle said as his eyes took everything in. Everything behind Barry was blurred.

"No, look here," Joe said as he pointed at an unusually distorted image a few paces behind Barry. "I think that's our 'ghost'," he said as he emphasized his point with finger quotes.

"Couldn't that just be glare?" Diggle asked, wondering if the detective was grasping at straws.

"If it was, I don't think it could blot out an entire face – and not from different angles," Joe said. This, along with the evidence of signal jamming, was making it easier for him to tag the 'ghost' as their perp – or at the very least, a person of interest.

"I agree. This isn't just glare. It covers too much to just be an innocuous play of light. I never thought this was possible with visible light cameras," Cisco commented as he marvelled at the image. The most you could make out was that the figure was tall and in a hoodie. "This is hard enough to do at night, especially now that a lot of cameras come with anti-blooming technology," he continued as he pointed at the interesting light artifact that managed to blot out any distinguishing facial features on the figure, "It's kinda' cool to see it implemented well in daylight."

They continued to look at the feed as Barry and the ghost went out of frame.

"¡Dios mío!" Cisco exclaimed as he noticed something peculiar with the timestamps. "Felicity, can you cue up the CCPD feeds and run it alongside these new ones?"

Felicity nodded as her fingers went to work. The feeds started playing synchronously on her screen.

"What are we looking at here, Cisco?" Caitlin asked impatiently. Her brain didn't have the patience for show-and-tell – not when she had mountains of her own data waiting for her.

"See these?" Cisco said as he pointed out the timestamps on the CCPD feeds just as they cut to white noise.

"The source of the signal interference seems to be moving," Oliver concluded as he took in the snowy black screens as they cut back to clear moving images.

"Yes, and look at how it tracks," Cisco said as he circled his fingers on Joe's ghost through the other CCTV feeds.

"Oh my God!" Felicity yelped as she almost fell out of her seat, "I have to verify my calculations but the 'ghost' could be the source of the interference!"

"And that right there, tells you that whoever this is knows how to defeat multiple surveillance systems," Cisco said.

"That still doesn't mean Barry was being followed," Digg commented.

"Don't you think it's too much of a coincidence – having someone with mad counter-surveillance skills lurking about?" Cisco argued, as he looked to Oliver to settle the debate.

Oliver's brain agreed with Digg but his gut was with Joe and Cisco. "It's suspicious, yes. But we need more information." He turned to Joe then and asked, "Any eye witnesses?"

"We canvassed the area. No dice. The camera on the slushie truck has been broken for months. We got hold of a few customers but they didn't spot anything out of the ordinary. The staff identified Barry but really didn't notice anything weird with him. They did tell us it was a busy morning so they really couldn't tell for sure. The one manning the counter identified a regular customer who stood behind Barry in the line. Eddie and his team are tracking him down as we speak."

"So, what now? We don't have anything useful enough to feed Felicity's facial recognition software and we have no credible witnesses," Caitlin exasperatedly pointed out.

"Wait. We might not have enough for facial recognition but we may have just enough here for something else," Felicity said as she abruptly stood up and went over to the knapsack she had brought over from Starling City. She retrieved another portable hard drive and plugged it into the computer terminal she was working on.

She started to type several commands into the terminal and brought up the interface of a program Oliver recognized from her presentation at Queen Incorporated's product roll out meeting. "Is this…" Oliver trailed.

"Proprietary software – I know! But before you say anything, we could really use a proof-of-concept test for this subroutine and this is it. And I'm running it offline within S.T.A.R. Labs' firewalled firewall," Felicity said, as she finalized the set of commands she wanted to run. She turned to Oliver as she finished typing the last line, pleading with her eyes for his final approval even with her finger already itching to execute what Oliver knew to be the "capture sequence". She usually wouldn't have thought to ask permission because the program was her brainchild anyway, but Oliver still owned most of the company which stood to lose millions upon millions of dollars if this top-secret patentable product were to leak.

Oliver nodded, "Okay, now's a good time as any."

Felicity hit the "Enter" key at his say so and started the sequence.

"Are you for real?!" Cisco erupted once he realized what Felicity's program was doing. Felicity just smiled at him and nodded.

"Care to share with the class?" Digg huffed as the program started capturing several images of the 'ghost' walking from what footage was available to them. It was sometimes necessary to remind his friends that not everyone was a genius.

"Say hello to gait recognition software! There's a race to get this off for real-time surveillance because in theory, unlike fingerprints, iris scans and facial recognition, gait doesn't require as much cooperation from the subject and biometric data is preserved even at a distance from the sensor. The downside is that recognition can easily be thrown off by different shoes, baggy clothes, a change in walking speed and the like," Felicity explained as she continued to run the video feeds through the capture sequence. "But I tweaked this baby to minimize those distortions by selecting several invariant features and using these to create a single composite silhouette."

"Okay, I get it. But how will we get an ID if there isn't a database to compare this image with?" Joe asked.

Felicity held up a finger as she fed the last of the videos through the capture sequence. A single image appeared on the screen a few seconds later, "We can use this to build a probe library. If you can give us stable and secure access to the city's CCTV feeds from traffic and street cams and assuming this system can handle petabytes of real-time data, I'll be able to scour them for any gait that matches this. We may not be able to get a name but we can track the 'ghost's' movement if any, and get to the bottom of this."

"These babies can handle that and more," Cisco said as he patted the computers on the terminal. "We could also use the probe to look through the last few days, see if Barry was really being tailed or not."

"Then we scour every second of Barry's day today and start working back from that," Oliver said. "Expand our search area and his timeline."

Cisco nodded but before anyone could voice out anything else, Joe's phone rang. "I'll have to take this," he said as he stepped away from the bank of computers.

"Do you guys have any other leads we can follow until we get access?" Oliver asked Caitlin and Cisco.

"Joe has just given me Barry's lab results," Caitlin said. "I still have to see how they line up with my own tests." She wanted to give her data another look before she stated her conclusions. As it were, things don't really look good.

"And I just got Barry's hard drive. I still have to look at it, though. Hopefully, it isn't heavily encrypted," Cisco reported.

"Eddie tracked down the witness. He's down at the station working with a sketch artist," Joe announced as he clicked off his phone. To Felicity, he said, "I'll head on over there and see about your access to our feeds. I'll keep you posted." With that, the detective took his leave, and with a last look at Barry's treatment room, he left.

After each giving an acknowledging nod toward the departing man, everybody went back to their own stations: Digg went back to Barry's room, Cisco moved to his worktable and started to look at Barry's hard drive, Caitlin headed back to the mouse lab and Felicity sat back down and started working several masking filters into the program. Oliver was left standing in front of the embankment, feeling a little bit lost – not knowing really what to do with himself. He was the muscle apparently, and there was nowhere he was needed yet.

His forefinger started rubbing against his thumb.

"Hey," Felicity said when she took his right hand in one of hers, effectively stopping his tic. She brought him down on the chair that Caitlin had vacated beside her. He looked at her then and found her giving him a knowing look.

God help him if he thought he could hide anything from her.

She rolled her seat towards him and used her free hand to reach for the other keyboard. "I need your help," she said as she squeezed his hand reassuringly and placed the keyboard directly in front of him.

He brought her hand to his lips and kissed her knuckles, "Anything specific?"

"I need you to look through all this footage and mark anything that trips your spidey sense," she winked at him and smiled as she let go of his hand to return to her own work.

Oliver chuckled while he faced his own computer and said, "You got it."

Thanks so much for still reading! I know I've been slow to update. Anyway, there's quite a few more chapters to go here, so stay tuned! Kisses!