A/N: Oh and I updated chapter 3 to put in the line breaks because I forgot. What?! I'm updating a couple days later instead of weeks?! Time to find out who the mystery person is. Thank you for all the reviews keep them up I may update again in a couple days. Remember the more reviews the faster I update!

"It isn't, is it?" They both turned and faced each other as they said it at the same time.

"Hey guys look who showed up from downstairs," Ryan smirked.

"It's our old friend Demming," Esposito added with a grin on his face.

They were loving every minute of this. For the second time today Castle was speechless, and that never happened. He knew his and Beckett's relationship was solid and there was no real reason to be jealous but he just couldn't help it. He's a guy. Plus, seeing Demming brought up memories from the past. He can't help but blame Demming that he and Becket didn't get together 3 years ago. If he wasn't around back then, then maybe she would've said yes to going to the Hamptons and the whole disaster between him and Gina never would've happened. But that doesn't matter anymore. Demming let her go, so Castle wins. He knew that last thought was childish but he is a child at heart. Besides thanks to Esposito and Ryan putting those noses in Beckett's relationship when they went into the Hamptons for the weekend, he knew that Demming was dating someone else, so no reason to be worried. None. At. All.

"Hey Demming, how have you been?" Castle stuck his hand to shake it. What he really wanted to do is pull Beckett closer to him and wrap his arm around her but that would backfire on him on so many levels.

"I've been good man, how's the books going?"

"Oh you know I write them, people buy them; same old-same old."

"So how's it down in robbery?" Beckett jumped him before they pulled down their pants right there in the middle of the precinct.

"Better than up here, more interesting cases, although I do miss that coffee machine you bought, Rick."

"It's still in the same place, I want a cup myself come on let's go," Rick offered, they went to the break room leaving Beckett and the boys to catch up on the case.

"So...Demming's back. That's got to be awkward," Esposito said.

"Yeah. You're really going to let them go in there without you?" Ryan chimed in.

"Okay guys. Not that it's any of your business but, Castle and I are in a good place and Demming is not going to mess that up besides they're both grown men. They know how to behave." Esposito and Ryan gave her a look that said you-really-believe-that? "Well one of them is a grown man that knows how to behave." She narrowed her eyes at them, saying mind-your-own-business. "Now what did you find out about the husband?"

They moved on, knowing that pushing it further would just end up with more paper work on their desks. "Well, we checked with the people in his office and they said he always stays late and they all leave before him, so it wouldn't be unusual for him to stay the night because he' s done it before."

"So basically no one can say for sure if he was there all night, that means he's still on our list." She said putting his picture under the suspect's category on the murder board.

"Well not exactly, the floor and elevators have security cameras so they're sending it over, I'll take a look at it to see if it shows him leaving," Ryan offered.

"Alright good work guys, I also need you to look into the couple, Zoey and Adrian. Oh. And Zoey's mom Renee. A witness told us that they might hold a grudge against our vic."

"A witness? What witness? The neighbors didn't see anything." They stood together arms crossed, staring at her, silently asking what aren't you telling us?

"Right… well, guys...this case is a personal one... for Gates."

This got their attention, "Gates? A personal case? What's the whole story?" They stood together, arms crossed.

She told almost the whole story, instead of telling them Gates caught them at her apartment, she told them Gates called her. She was not about to tell them the real story. They would have a field day knowing the truth and she did not need to deal with them and their jokes on top of everything else.

"Now. I'm going to go catch Demming up and have him take the husband to his house, so he can tell us if anything is missing."

They watched her leave, they knew she wasn't telling them the truth; they are detectives after all.

"So what do you think really happened?" Ryan asked Esposito.

"I don't know bro but if she's not telling us, it must be good and I've got someone who will know." They did they're fist bump handshake and went to work.

"So you and Beckett are together..." Demming brought up while Castle made their coffees. "What's it been? About 3 years now?"

Castle turned and stared at him, "No. It's only been less than a year. Why did you think it was 3 years?"

"Well you know when she broke up with me; I knew it was because of you even though she wouldn't say it. I am a detective; I know how to read people."

Castle could tell he was missing something, "She broke up with you? When was this?"

"Oh I don't know right before summer 3 years ago."

Castle thought back summer three years ago, that was the summer before she was shot. Then it hit him that's the summer he asked her to join him in the Hamptons and she turned him down. He remembers they were talking but interrupted by Gina, was she about to tell him that she wanted to go with him?

Before he could think about it further and question Demming further, Beckett walked in, "Hey Demming, you ready?"

"Ready? What are you guys doing?" Castle jumped in, he chastised himself once he saw Beckett's look of not-right-now. He didn't mean to sound jealous especially since the information he just pieced together but he's Beckett's ex and no matter what there would always be a bit of jealousy when it comes to Demming.

"I'm just catching him up on the case and introducing him to the husband so he can take him to the crime scene."

"Oh... okay," he said; now feeling like an idiot. He gave her his best I'm-sorry-please-don't-be-mad look. She smiled back. Everything was okay between them. Not that he was worried to begin with.

Once she caught him up on the murder board and introduced him to the husband, she went back to her desk where Castle was sitting as patiently as possible for her.

"Hey ready?" He was cut off by ringing of her phone.

"Beckett...uh huh...okay thank you." She had her professional detective voice on. "That was CSU they found a matching set of prints on the murder weapon and the back door. No matches in the system but if we find our suspect then we can see if they match. What were you about to say?"

"I was just going to ask if you are ready to go home?" Castle asked eagerly.

"Castle we're in the middle of a case, why would I go home now?"

"Because there's nothing else to do right now, your following all the leads you can. All you're doing is sitting here waiting for information when you can do that home, besides it's nine o'clock, they won't find anything else tonight, if they do they can call you."

She bit her lip as she thought about what he said. It's true. There wasn't really anything else she can do right now and she just wanted to go home curl up on the couch with a glass wine and a good book. "Alright let me just shut down my computer and grab my jacket then we can go," she conceded.

She sat on the couch her legs tucked underneath, her hair undone, falling down her shoulders. She felt almost relaxed the only thing she needed was a glass of wine.

Castle was in the kitchen pouring two glasses of her favorite red wine. They were going to need it until this case was over especially now that Demming was a part of it. This case was just becoming too much. Gates's mother in law, Gates catching him at Beckett's apartment, and now dealing with Demming. How was he supposed to handle all that? He trusted Beckett and knew there was no reason to worry about them two. After pressing the boys for more details, he knew Demming was seeing a vice detective for several months now. He found it interesting that he's now dating someone in vice and Beckett used to work in vice.

He sat down next to her, handed her the wine. "So…Demming's back." Castle cautiously brought up.

"Yeah. For this one case. Look, Castle, if we're going to work this case together then I need you to behave and keep it professional. I don't want to give Gates a reason to kick you out by letting your jealousy get the best of you."

"Me jealous? Ha!" She looked at him. "Alright fine I was a little jealous when he showed up but I know everything with him happened a long time ago and I trust you. Besides he's dating a vice girl." He added as he took a sip of wine hoping she wouldn't catch that last part, but she wouldn't be Beckett if she didn't.

"How do you know that?" Kate asked suspiciously.

"How do I know what?" He knew that not only would he get in trouble but also Ryan and Esposito, if that happened they would never do him a favor again, even if he offered them the Ferrari for a year each.

She rolled her eyes; he could play dumb all he wants she knew that Ryan and Espo told him and they probably found out when they butted into her life when she went to the Hamptons with Castle.

"Okay well I was thinking about the vow renewal, and I know there was that couple who was trying to book everything they wanted so they had the wedding of the season. My money is on them or her mom; weddings can be very expensive and make people go crazy, trust me going through two of them myself. I've learned it's best to just let the bride make the decisions and not stand in her way. This one time some girl wanted the same veil as Meredith and there was no way she…" Castle cut himself off when he looked over and saw Beckett with that look that says better-stop-now-before-I-get-my-gun. "Anyways the point is weddings make people especially brides do something they would never do."

"Well Ryan and Esposito are looking into them, so hopefully we'll know more tomorrow about it."

She stood up and walked towards the bedroom, turned around in the office doorway her eyes turning a dark green, the shade he knows only means one thing, "I need to relieve a little stress after today so will I be relieving it alone or..." she was cut off by Castle jumping up and swooping her up in his arms fireman style. "Castle" Kate said in an exasperated, husky tone.

"Don't you even finish that thought," Castle growled in her ear.

A/N: Okay so everyone who guessed, was correct. It was Demming dun dun dun...