Author's Note: I'd like to thank southerngirl1, phnxgrl, MaineCastle, and Chkgun93 for their reviews. I'm so glad to be back too! Glad you guys loved the Castle theories. This chapter starts not long after the last one left off. Enjoy!

Chapter 11

Beckett had left the interview with Mrs. Conklin feeling uneasy. She'd had no easy answer to the question of what had happened to John Conklin that wouldn't have hurt his wife more than necessary. Half the reason was the traumatic way he'd been killed; the other half was that Beckett still didn't know how things had happened in the first place.

Beckett set up the murder board differently this time. Normally the victim was the center of focus because the victim was usually the target. This time though, Conklin had been an unlucky bystander to whatever had happened in the sewers. If they were going to figure out who had killed him, they had to figure out who had set things in motion.

Castle handed Beckett a coffee as she stepped away from the board. "There are a lot of holes up there."

"There usually are at the start of a case."

"I mean, more than usual."

She sighed and leaned against the edge of her desk. "I know. Hopefully the lab can fill in a few of those blanks. I want to know what kind of explosive was used so we know whether the Feds need to be involved or not. Gates agreed to hold off on calling them in till we know if the explosion was intentional or a result of gases building up because the covers were welded shut."

Castle set his coffee down. "You think the explosion might have been an accident?"

Beckett shrugged. "Who knows? The manholes lead to the sewer main. Sewage produces methane gas, which is flammable. The welder could have simply wanted to prank the Sanitation Department by welding the manholes closed."

"If that's the case, then the explosion was an accidental byproduct of the prank." Castle nodded in understanding. "I see your point. How likely do you think that is?"

"Slim to none, but the possibility has to be kept open until it has been eliminated." She stood. "Hey, Ryan, have you found anything yet?"

"Give me a few minutes; the footage just started coming in."

"Okay, keep me posted."

He nodded. "Will do."

She settled into her spot again as she thought out loud. "If it was all on purpose, what were they trying to do? What was the point?"

"My first thought is trying to blow up a street." Castle stood and pointed to the photo of the manhole cover. "The manholes were welded into place, probably to prevent the gases and explosion byproducts from taking the easy way out. If this cover's welds hadn't failed, who knows what might have happened."

Beckett set her coffee down. "Let's say we go with that. Why that street? It's not in a heavy traffic area."

Castle snapped his fingers as an idea hit. "Maybe it was a dry run. A way to see if the theory would work."

"Okay, but why? What is the bomber hoping to accomplish?"

"I got nothing."

"Nothing? That's not like you; normally you have something that feels like it came out of left field. Kind of like your theories this morning."

Castle smirked. "Okay, maybe it's more like I have too many theories."

"Such as?"

"Anything from holding the city hostage by creating the worst gridlock in the history of New York to seeing if they could recreate the sets from 'The Avengers' after their battle in Manhattan. The point is my theories are probably not going to help at the moment."

Esposito walked in. "Covers on three straight blocks were welded shut. They were only on the one street though. I've got a team checking out the sewers right now."

Beckett nodded. "Bomb squad is going in first, right?"

"Yeah, they're doing the initial sweep, checking for more explosives, bomb parts, that sort of thing. We should know more in a few more hours."

"Good. Go help Ryan screen the footage of the area. Three blocks is a lot of stuff to look at."

"You got it." He turned and headed toward his desk. "Hey, man. Welcome back."

"Thanks. And thanks for the decorations. Took me five minutes to find my keyboard."

Esposito laughed. "Don't lie, you know you like it."

Beckett smiled at her partners' banter as her phone buzzed with an incoming text. "Lanie's got something for us."

"Hey, Lanie, what'd you find?"

"Let's start with you. What'd you find out about my vic from the family? It might help me put my findings into context."

Beckett pulled her notebook out of her pocket. "He was a stock broker who dealt mostly in foreign markets. Why?"

Lanie held up Conklin's arms. "See the small burns around the forearms and hands? If he was in construction, I'd say these were injuries from his job."

"What causes them?" Castle had leaned down to take a closer look and was now looking up at Lanie.

"These look like burns welders have when their safety equipment is in bad shape or they don't know how to use the equipment." Lanie set the vic's arm back on the slab. "These burns are recent too, only a couple days old. I'm not gonna say it, but Mr. Conklin here might have been the welder you're looking for."

"That doesn't make sense." Beckett pocketed her notebook. "If he was involved in a bombing plot, he wouldn't have taken that route home."

Lanie held up her hands. "I'm just telling you what I found. Anyway, cause of death is atlanto-occipital dislocation, also known as internal decapitation. The manhole cover hit him on the upper back with enough force to give him a major case of whiplash that separated his skull from his spine and severed his spinal cord. Death would have been mercifully quick and relatively painless."

Beckett raised an eyebrow. "How would the cover have hit him there?"

"Fractures around his knees and ankles tell me he may have been crouched when he was hit."

Castle turned to Beckett. "His body was behind a car. The cover shooting into the air probably scared him and he took cover behind the closest thing he could find."

"It just happened to be right where a manhole cover would land." Beckett nodded and turned to Lanie. "Anything else I should know about?"

She pulled back the sheet to reveal Conklin's mangled chest. "It's hard to tell through lividity and everything else that happened, but it looks like Conklin might have taken a beating in the last few days."

"What makes you say that?"

Lanie pointed to some patches that were slightly darker than the surrounding areas. "I noticed this. It seemed a little odd despite the manner of death, so I decided to take a closer look." She handed Beckett a folder. "The infrared shots make it clearer. You can see fist-shaped bruises. I'd say these are about four days old."

Beckett flipped through the photos. "I'm going to have to talk to the wife again. When we spoke to her earlier, we thought it was just an accident. Now I have a few more questions."

"One last thing." Lanie held up a small evidence collection dish. "I found these in his shoe. I'm not sure what they are so I'm gonna send it over to the lab. Maybe they can tell us."

"May I see?" Castle took the dish from Lanie and held it up. "These look like chads you might find at a racetrack."

Lanie took the dish back. "Chads?"

"Yeah, the little bits of paper that get punched out of a card. I doubt his workplace still uses punch cards, and the elections here are done electronically, so a racetrack is more likely."

Beckett closed the folder in her hands. "I'll add that to the list of questions I have. Thanks, Lanie."

"You got it."

Beckett and Castle returned to the bullpen and updated the board. If Castle's identification of the paper bits was right, it looked like Conklin might have a thing for the ponies. That could mean he had a gambling debt if the bruises were anything to go by. Beckett wondered if Conklin's involvement was involuntary. There was a possibility that something more was going on.

Ryan waved her over. "I think I found the welder, but it looks like he's our victim."

Beckett took a look at the freeze frame. "Yep, that's him. Lanie found welding type burns on his wrists, so I was expecting this. Okay, new task. Look into Conklin's financials. I want to know if there was a reason he did this."

"Like a debt that suddenly got erased?"

"Yeah, exactly like that. Where's Espo?"

Ryan shrugged then grimaced. "He was watching his section of the footage, then said he had to check something."

"You okay?"

"Yeah, it's just the scar."

Beckett tapped her chest. "I know what you mean."

Esposito walked in. "Hey, Beckett, got the CSU report. Well, an early report anyway."

"Let's hear it."

"Once the Bomb Squad determined there were no more devices, CSU went in and took photos and a video. At the moment, they're labbing everything they collected, but I got the evidence recovery video and their early report."

Beckett leaned against Ryan's desk. "What'd they say caused the explosion?"

"Not sure yet. Things were scorched, but they couldn't find any bomb parts. Their early guess is that the event wasn't an explosion; it was a gas deflagration."

Castle put his hands in his pockets. "They're sure it was a deflagration and not a detonation?"

Esposito passed the folder of photos to Beckett. "There's a burn pattern on the walls that show the path of the flames. CSU and the bomb squad said a detonation would look different."

"I see." Beckett was flipping through the photos. "There is a lot of debris in here. Was this brought in or already there?"

"Already there, apparently. The sewers have a lot more in them than just sewage. Household waste and debris ends up down there too. The debris can come from storm drains, things dumped down an open hole, items workmen accidentally leave behind, and especially items that get flushed down the toilet."

Beckett nodded. "So it'd be hard to tell if…"

"Mythbusters." Everyone turned to Castle. "I was trying to remember where I'd seen this scenario before. The Mythbusters tested this myth a few years ago. Minus the welding of the covers."

Beckett closed the folder in mock finality. "That settles it then. Go pick 'em up. Oh, wait, they're based in San Francisco and do whatever they can to not cause stuff like this."

"I'm not saying Adam Savage and Jamie Hyneman are behind this. I'm wondering if their episode might have been the inspiration behind this. If methane is the gas that was burned, I'd say our bomber, or bombers, were inspired by the Mythbusters."

Esposito looked mildly impressed. "It's a theory. And not a bad one at that."

Beckett headed for the board. "We're going to need more than a theory to find the perp. Ryan, fill Espo in. Dig into our victim's past. I want to know why he was our welder."

Castle grabbed his coat from his chair. "Are we headed to talk to the wife?"

"Yep. She might be able to fill in some of the blanks."

A/N: If you can't guess from the last little bit, a Mythbusters episode kinda helped inspire this case. Drop a comment in the box below! Thanks!