Disclaimer: I don't own Castle or anything to do with it.

Chapter 7

The next morning Castle came in a little early. He handed Beckett her coffee which she took with a smile and a thanks. He glanced over at Rysposito both of whom looked clearly disappointed that their theory was a bust. Smith was to come in shortly for questioning.

There were still too many questions to answer. Why did the murderer have Smith's key card? Who had White recognized that night? What was with that Godforsaken symbol? And although Castle had his theory, there was still the lingering question about the motive behind both murders.

Smith arrived shortly and was escorted to the interrogation room. Beckett and Castle went in there with all the questions looming above them hoping for at least some answers.

"Mr. Smith, I'm detective Beckett and this is Castle. You dealt with our colleagues Detectives Ryan and Esposito yesterday. As they informed you, the murderer had entered the lab with your key card."

"I don't know how, but it was stolen. After the other two detectives came to me yesterday, I checked my bag, asked them to check it too. It wasn't there. It was nowhere in my house. You don't need the card to go out of the lab, only to enter it. So it's possible that the key card got stolen sometime that I took my eyes off my bag. I never kept it on me. And you have my alibi too" Smith finished nervously.

"Okay. That might be true, or there might be another scenario." Beckett stated.

Castle continued "You could have left for your house anytime between 12 and 1 am. Your neighbor had already told you to keep it down, which you probably did. So if you got out after that sometime when the women might've fallen asleep, you – a genius researcher could have easily distracted the night-guard and snuck out of your building. All you had to do was carry your key-card and a spray can which you'd have gotten ready earlier and dress inconspicuously. Dark glares, dressed in black over all, no one would have recognized you. Sure White was surprised if just for a minute and then she got back to her work because she recognized you. You had the added benefit of knowing where the cameras are so it was easy enough to take care of that. Then you kill her – the woman who had been insulting you for years and just walk out of there. Somewhere along the way you dump your key-card before sneaking back home" he finished.

His story was so convincing that Beckett considered it could actually be possible. She knew better though, taking all things into consideration but she saw that even Smith considered the scenario as he visibly paled and got completely nervous.

"N-no. That's not what happened. I swear" he stammered.

Beckett banged her hands on the table causing him to jump back "Then tell us what did happen Mr. Smith. It's your key-card we found, it's you who she recognized isn't it? Just tell my why you did it. Why kill White, why kill Wilkins?"

"Wilkins? I didn't even know him personally. Only what I saw of him on T.V." he said slightly stuttering as he spoke.

Just then Ryan walked in and placed a laptop so they all could see. "This is the camera footage. We went over it again and found a profile – of you." He pressed play and they did indeed see him as he momentarily lowered his glares.

"That's – that's not possible. You can ask the girls. We didn't do much sleeping. Someone must've tampered with the footage or something" he was now positively alarmed.

"Technology isn't that advanced Mr. Smith. Someone can't just 'insert' you in a video so easily" Castle said.

"But this isn't poss-" He suddenly said as his eyes widened. He went even paler if at all that was possible. He started shaking from head to toe. He spoke with a shaky voice but one that wore conviction "That isn't me."

"We've been over this – " Beckett said.

"No, you don't understand. That isn't me. It's my brother Daniel. My twin."

They all stepped out of the room leaving Nathan Smith alone. They needed a minute (or a few days) to regroup.

Castle spoke first. "A twin brother who's on a killing spree? This is more convoluted than – than –"

"Than one of your books?" Esposito said, fist-bumping Ryan.

"Har har." Castle replied dryly.

"It does seem far-fetched" Beckett added "But it's possible. We'll get back in there, ask him further questions. You guys go check this stuff out." She took a deep breath before getting back inside along with Castle.

"Tell us more about Daniel." She said as she sat down.

"The last I heard from him, he was in the military. He was always the smarter amongst the two of us." Nathan said.

"Smarter than you?" Castle asked.

"Yes. I worked really hard to get to where I am. Long hours, sleepless nights of studying. But he got ahead in life very easily. He had a photographic memory. He wasn't as emotional as me. He was even more athletic than I could ever hope to be. Right since we had kids head had a knack for manipulating people. His charm and knowledge propelled him in every field. He started at a prestigious university in the field of genetics just like me, but he dropped out in his second year to join the military. He said he could use his skills on more important things like protecting our country. After that he more or less stopped communicating with us, save for the letters we exchanged."

"What did he say in his letters recently?" Beckett asked.

"He had told me that initially they took him on in one of their research divisions but once they tested him on the field, he came out with flying colors of course. Eventually he was out of research and on the field permanently. Initially it sounded like he enjoyed it, said that it gave him an adrenaline rush like never before. But then his letters started changing."

"Changing how?" Castle asked.

He looked at his clasped hands and replied "I don't know exactly. Something felt off. He'd always been good at hiding his feelings. Like I said, he wasn't emotional like me, like most people. But I could sense it – maybe it's that twin bond thing people talk about. Sometimes he sounded agitated, sometimes he didn't talk about work at all. I asked him in my letters but I never got a straight reply from him."

"Have you heard from him recently? Did you know he was back?" Beckett asked.

"No, I had no idea. The last letter I got from him was about 8 months ago."

They heard a knock from the mirror. Beckett went to the door as it opened just a bit. Castle correctly presumed it was to confirm everything Nathan Smith had just said. Beckett told him he was free to go, but that if he heard anything from his brother, he was to call her immediately and told her to hand all the letters to them.

The rest of the day was spent in trying to find out more about Daniel Smith. It wasn't easy. Whatever it was that he did in the military, they weren't too forthcoming with the information. By the time they did the scut work to make the military comply, it was nearing night and they would only have their information the next morning, along with the letters Nathan Smith said he'd find and hand over.

"There's nothing more we can do today guys. I'll see you tomorrow. Get some rest. This thing is turning out to be a huge headache." She said and saw them nodding their heads.

Castle saw as she wore her leather jacket. He bent forward a little to see her helmet under her desk. She had brought her bike.

"Ooooh Beckett. Do I finally get to ride your bike with you? Please? Pretty please with a cherry on top?" He asked Beckett enthusiastically. She couldn't help but smile at her writer man-child. Her writer man-child? When did she start thinking that she wondered.

"Do you have a helmet?" She asked.

"No. Why would I?"

"Then no rides for you tonight Castle." The second she said it she realized she should have been more careful with the wording. Judging by the smirk on his face, he was thinking along the same lines.

"Okay detective. Too bad. I'm sure it would have been great" he said in a low voice that caused a blush to sneak up her skin. Score Castle-1, Beckett-0.

She had to regain control. "Next time carry your helmet."

"Oh I'll carry it every day from now on" he said. "Next time I'll be prepared." Score Castle-2, Beckett-0.

She was off her game tonight, she just handed those to him in a platter. She was too tired to think right now anyway and thought it better to part. She'll get him back for this. "Good night Castle" she said firmly as she paced ahead to get to her bike.

"Until tomorrow, detective." He stayed back and watched her mount her bike and put her gloves on. He also noticed someone else dressed in all black on a bike looking like he was waiting for someone. He couldn't help but be slightly worried but he chalked it up to paranoia. He was always a little paranoid these days about her safety.

As she revved her bike and started though, he saw the man in black do the same and follow her. He tried calling her once but knew that she might not hear it while riding her bike. He called the boys.

"Espo, I think someone's following Beckett" he said as Esposito cut his call. He turned around to see that Esposito and Ryan were just behind him. They must've just been about to leave too.

"Which way did they go?" He said as all of them stepped toward their car. Castle pointed out and said that she was headed home.

"Let's go." They all sat in the car and made to follow her.

Castle wasn't the only one paranoid about her safety. There was only one person more paranoid than he was, and that was Beckett herself. She's a trained detective who knows when she's being followed.