Author's Note: I'd like to thank phnxgrl, southerngirl1, MaineCastle, and Chkgun93 for their reviews. Chkgun93: Sorry, we won't be getting to see Castle trying to convince Gates. I tried to do it, but Gates always said no for some reason :). MaineCastle: this will be a more serious Martha in this chapter. Normal Martha hijinks would kill the sting and she doesn't want to get her son in trouble again. Anyway, we're starting this chapter at the beginning of the sting. Enjoy!

Chapter 16

It had taken some work, but Gates did finally approve of Martha playing the bait for the sting. Tory was busy setting up some equipment in the Conference Room so they could track the call Martha made. The NYPD Taxi Squad had lent them a cab for Martha and Esposito to use while they followed the instructions and an undercover Bomb Squad unit was going to follow a block behind them, just in case. Martha was preparing herself in the loft with an undercover officer who was ready to pose as her assistant if necessary. The rest of the team was in the Conference Room, waiting for an address from Tory.

Tory finally stopped plugging things in and checked her screen. "Okay, we're set up."

Back at the loft, Martha took a deep breath and dialed the number. "It's ringing." She made sure to hold the phone on her right side where her earpiece was so the team could hear everything too.

On the fourth ring a man answered, his soft voice an unexpected sound for them all. "Yes?"

Martha decided to play up the nervousness. "Um, yes, I got this number from an, ah, associate. He said you might help me."

"What's his name?"

"Gretkov," Martha spoke in a whisper, then cleared her throat and spoke louder, "his name is Gretkov."

"What do you owe him?"

"$5,000. And the debt is due. Please, can you help me? I don't know what I'll do if you can't. He said he'd hurt my granddaughter if I don't pay him."

Tory snapped her fingers and pointed at the screen. They had an address. Beckett, Castle, and Ryan left the Conference Room and took the stairs down to the car. In the meantime, Martha had been given an address to go to and she was headed down to meet Esposito in the cab.

Beckett, Castle, and Ryan went as fast as they could without turning on their lights or sirens. Their vehicles were followed by two blue and whites, but that was all the backup they could get without putting a call out over the police bands. They were worried that the target might have a police scanner to keep tabs on his minions' progress, success, or failure. If he had a police scanner, it was also possible that he could listen in on their wiretap. So far, it seemed like he couldn't, but they still were barely using their radios so they could stay as off the grid as possible in order to catch him.

Half an hour later they arrived at the address as Martha made her second call to him. "Okay, I'm here. What am I doing here?"

"Do you see the green dumpster at the end of the alley?"

"Which alley? There are two."

The man on the other end of the call sighed. "It's the alley next to the Chinese restaurant."

Martha sounded like she was moving quickly. "I see the alley…I see the green dumpster."

"Are you at it?"

"Give an old woman a minute, I don't move like I used to. Okay, I'm there. Now what?"

"Behind the dumpster is a black duffel bag. Take it to the alley between 8th and 9th at 320 West 19th."

Martha grunted as she lifted the bag. "This is heavy. What am I to do with it?"

Martha didn't get an answer. The call had ended abruptly, just like Sheppard had described it. Seconds later Beckett received a text from Tory. Because she'd had a smaller area to search this time around, the I.T. Analyst had been able to narrow it down to an apartment this time. Beckett had Ryan pull up the floor plan of the building so she could direct the uniforms to their posts.

Beckett covered her microphone; Martha didn't need to listen to her directing the troops. "I want you to go up the fire escape and wait a floor below his window." She was pointing as she talked. "I want you to use the roof access or go through an apartment on the top floor to get to the fire escape a floor above his place. Be as quiet as you can." The pair from one of the blue and whites nodded.

She pointed to the other partnership. "I want you two to split up and cover the staircases at either end of his floor. If he gets past Ryan and me, it'll be your job to make sure he can't get out that way. Ryan and I will take his front door."

Castle held up his hand. "What about me?"

"You'll be holding the elevator at the ground floor. Same thing I told the last pair; if he doesn't use the fire escape and gets past Ryan and me, I don't want him to have that option available."

One of the uniforms raised his hand. "When do we breach?"

"You won't be breaching. You're there to cut off an escape route. If he comes out the window, you'll be there to stop him." Beckett looked around. "Any other questions?"

Nobody had another question and so the groups split up. Castle let the uniform positioned above the window to ride the elevator up to the top floor before calling it back down and standing in the doorway so it couldn't go up again. Ryan and Beckett took the stairs to the fifth floor with the uniform that would be covering that door and waited. Gates had gotten them a no-knock arrest warrant and Beckett planned on going in while the suspect was on the phone with Martha. That way, no lawyer could say the arrest was based on conjecture.

Beckett and Ryan waited on the landing of the stairs until they heard Martha call again. "Okay, I'm here. What am I supposed to do now?"

Beckett and Ryan made their way to the apartment door as their target spoke again. "Open the duffel bag."

Martha gasped. "What is this? It looks like a bomb."

"I know that's what it looks like, but it isn't; at least not the traditional kind. Now, put it under the intake vent of the building on the right. The vent should be behind the dumpster."

At this point, Martha had been instructed to not follow the directions. Beckett knew Martha would be handing the bag and device over to Esposito, who would give it to the bomb squad officers for containment. She nodded to Ryan who took his position on one side of the door. Now they had to wait for word from Martha.

Their target was getting impatient. "Well?"

Martha was breathing heavy. "Sorry, that was heavy for an old woman like me. It's in place. Will my debt be paid?"

"Of cor…"

Beckett kicked the door in. "NYPD, don't move!"

Through her earpiece, Beckett could hear a phone hit the floor and the call ended. Deeper in the apartment Beckett could hear a man scrambling for the fire escape. A window was thrown open, closely followed by yells announcing the presence of the two uniforms waiting outside. A curse was followed by the sounds of furniture falling over. Beckett entered the bedroom with her gun drawn to see a stereotypical nerd sprawled on the floor with the uniforms looking in at him from the window, guns drawn.

Beckett holstered her piece, cuffed him, and hoisted him to his feet. "You're under arrest."

"It's too late. The device was detonated."

"Esposito, was the device secured?"

"That would be correct. Bomb Squad is working on the containment box right now. Martha and I are a safe distance from the unit and our uniforms have secured the perimeter."

Beckett turned back to their suspect. "Bad news, our people have your device locked up tight. No one is getting hurt today."

Beckett had one pair of uniforms take the suspect back to the precinct and run him through the system. CSU was called in to process the scene while Tory went over his computer to see what information they could use. Castle and Esposito were filled in on what had happened in the apartment; Esposito filled them in on what they'd done at the scene and what the bomb squad said the device was for. It was designed to release a nonlethal gas directly into the building's intake vent. Why was still a mystery, but they were hoping the computers in the apartment would shed some light on his latest endeavor.

Beckett walked into Interrogation with her folder. Inside was everything they had on Noah Kramer so far. He had been a graduate student at Northwestern studying Mechanical Engineering when he'd been expelled for "ethical misconduct." After that he'd dropped off the map for the most part until recently. Beckett sat down and looked at the man sitting across from her. Her initial assessment that he was a stereotypical nerd had been a little off. Kramer was bespectacled with slightly unkempt hair, but his clothes were new and clean. Not only that, they looked to be just a few steps down from being designer. Combine that with his alleged actions and Beckett could tell he was well off.

"Your device contained a nonlethal gas. What was the point of that?"

"That experiment wasn't over yet. I don't talk about my work until I have results."

Beckett nodded. "We have a team going through your apartment and computers right now, so I'm sure we'll figure it out. What about the sewer system explosion on 52nd? Will you talk about that?"

Kramer looked disappointed. "It didn't work the way it was supposed to."

"What do you mean?"

"When Jamie and Adam did it, they didn't take the experiment as far as they could have. I wrote to them, told them they should try welding the covers shut, but they just ignored me."

"Why should they have tried welding the covers shut?"

"To see what could have happened!"

Beckett wanted to keep him talking, so going slow would be the best way. "What should have happened?"

Kramer sighed as though he was frustrated with her slowness. "It should have blown the street apart. I was trying to prove that the antiquated systems in most large and old cities aren't capable of handling the pressures that could be generated in the aging sewer systems."

"How does blowing up a street prove that?"

"Sewage produces methane gas. Methane gas is highly volatile. If the gas to air ratio is just right, a spark could set the whole thing off. The system doesn't have a way to syphon off the methane gas. I had the show why that is a bad idea."

Beckett sat back in her chair. "So why have John Conklin weld the covers shut? Why not do that yourself?"

Kramer hit the table. "To make a point! They say the squeaky wheel gets the grease, but that is a lie. I've been petitioning the city to update the system for years. You know how many times covers have popped off in that amount of time?"

"I'm afraid I don't."

"Nine. Nine times in the last three years covers have popped out of their holes because of pressure buildup. Thousands of dollars in private and city property damages, but the city never did anything. They just put the covers back where they came from. If it was city property, they'd fix that up, but if it was a car then tough luck. That's the risk of parking your car in the city I guess."

"So you'd had enough."

Kramer threw his hands up in a "finally" gesture. "Yes! No one was listening! I had to do something!"

Beckett pulled the DMV pictures of Conklin and Sheppard out of her folder. "So you paid off their gambling debts to get them to do your dirty work." She placed the photos in front of him.

"I never met them; just told them what to do over the phone." Kramer pushed the photos back to Beckett. "I couldn't risk getting caught. I'd never be able to finish my experiments then."

"How many 'experiments' have you conducted?"

Kramer smirked. "I'm not telling."

Beckett gathered up the folder. "You might not, but I'm willing to bet your apartment will. For now, you're under arrest for murder, conspiracy, and destruction of city property. When we're done searching your place, I'm sure the D.A. will add on a few more charges."

Castle and her team met Beckett outside I1. "I'm surprised he never asked for a lawyer."

"In his mind, he didn't do anything wrong. What'd CSU find in the apartment?"

"Enough to close the books on several open cases. Kramer is not going anywhere for a while." Esposito gestured to the suspect as he was escorted out of I1. "Now that we're done with him, other precincts and departments will get their turn to interrogate him."

Ryan nodded. "Almost a dozen detectives across the city are fighting to talk to him. D.A. is going to have his hands full for a while."

"I'm just glad we could get him off the street."

A/N: And that's a wrap for this case. The start of the next case will be next week or the week after that. In the meantime, drop a note in the comments box below. Thanks!