Mark is lying in bed looking at the ceiling. He normally doesn't have any trouble sleeping but this case has really gotten to him. Mark is toying with going against Brass and telling Catherine about the PI that was following her ordered by the undersheriff and paid for by Eddie. On the other hand, there's no need to cause Catherine any extra worry. Lindsey has finally gotten to a stage where she's not acting out anymore. Maybe Brass is right they should wait until they find out more. Mark looks over and sees Catherine sleeping. Mark gets out of bed and goes to the basement to work on the case.

Catherine rolls over and places her arm on Mark's side of the bed, finding it cold she looks around to see he is no longer in bed. Catherine checks the time and she still has several hours before she needs to be up. She listens in case he is in the bathroom, but hears nothing. Catherine gets up and puts on her robe in search of Mark.

Mark sets his case folder down and rubs his eyes in frustration.

Catherine coming down the stairs to the basement sees this and asks, "Hey babe you ok?"

Mark taking his hands away from his eyes replies, "Yeah I couldn't sleep so I thought I'd work for a bit but I need sleep because I can't concentrate on it."

Catherine walks closer to Mark and takes his hand and says, "Let's see if you can't go back to sleep. Come on."

A few hours later Mark is still tossing and turning.

Catherine rolls over and says, "Ok I've tried to ignore it but something is bothering you. I've noticed it since we came home the other day after you had been in Brass' office. What is going on?"

Mark sighs and responds, "I think it's just stress."

Catherine asks, "Are you sure that's it? You swear it's nothing with Brass?"

Mark chuckles and replies, "Well, honey it's not all Brass but he is involved in the cases I'm working on."

Catherine asks knowing it's a dumb question, "Do you want to talk about the cases?"

Mark replies, "Not really. I'd like my brain to shut off for a few hours."

Catherine smiles knowing the perfect distraction. She leans over, gets on top of Mark and kisses him.

Catherine looking down at Mark asks, "Is this helping?"

Mark grins and replies, "You know I don't know you may need to do it a few more times."

Catherine kisses Mark again eventually turning it into something more physical.

Later at the lab …

Mark is sitting in Sara's lab. This is one of the older labs that she uses to hide when she needs to think or work. Since Sara and Mark have gotten close she lets him use it at his disposal.

Sara walks in and says, "I guess you're having a bad day too?"

Mark looking up from his case files smiles and responds, "Yeah something like that."

Sara sits down and asks, "Mind if I join you?"

Mark laughs and replies, "It's your lab. I should be asking you that."

They work together in silence for a while.

Mark asks a question that has been on his mind for a while, "Do you think it's ok to keep things from someone until you find out more about the situation or if you think you're protecting them?"

Sara keeping her eyes on her case files says, "It depends on the situation. Does this involve Catherine?"

Mark sighs.

Sara says, "I'm only asking because I don't know if I'm the best for relationship advice. I'm not going to run and tell her."

Mark says, "Let's just say I'm working a sensitive off the record case with Brass and there's some information I think Catherine needs to know but Brass thinks we need to hold off until we have more information."

Sara says, "You're stuck between acting like a CSI and a boyfriend."

Mark says, "Exactly. What would you do?"

Sara responds, "Your relationship is new and you guys haven't had any big blowouts yet and you're living together so you don't want to rock the boat. Does Catherine suspect anything? She's not going to be happy if she thinks you're keeping something from her."

Mark sighs and says, "She knows something is up because I haven't been sleeping, but she hasn't pushed me on it."

Sara chuckles.

Mark gives her a questioning look and asks, "What?"

Sara replies, "Cath must really like you. She is a great person but she is headstrong. The two of us used to butt heads all the time. If she's not pushing you on your shit she must be trying to change her ways for you."

Mark laughs and says, "Her sister told me she was stubborn too. I haven't seen it yet. One thing is for sure is that if that's the case she's not the only one changing her ways. There are very few people who know all about me. You broke down those walls easily by trusting me with your coming out in the beginning and I felt comfortable telling you stuff. I want to tell Catherine everything but making yourself vulnerable and putting yourself out there is never easy once you've been burned before. With you I guess it's easier because we're not dating you know?"

Sara nods and responds, "I definitely know what you mean. Wanting to better yourself to be with someone though is a good sign; I think it's the start of something good, but you have to realize it's going to take time. "

Just then Sara gets paged.

On her way out the door Sara turns around and says, "Look for what it's worth Brass is a great investigator, he will rarely steer you wrong. Listen to him but also listen to yourself. But if you are going to do something make sure it's for the good of the case and not for your personal feelings. If it's what I think it is knowing what happened and closing it will do more good than letting emotions take over and potentially stop that from happening. Oh and let me know if you need anything."

Mark smiles watching Sara leave to get her results. Just then he gets a page from Brass to meet him in his office.

Brass is on the phone when Mark comes into the office. Brass motions for Mark to close the door and take a seat.

Brass hangs up the phone and says, "Sorry about that, some rookie apparently thought it would be a good idea to side swipe three parked cars while looking up a license plate."

Mark laughs and responds, "Sounds like you're having a good day."

Brass says, "Tell me about it. Have you found anything else out?"

Mark replies, "Yeah about a month before Eddie was murdered the payments stopped going to Sparky."

Brass says, "Ok I will follow up with him on that. Was there anything in his notes on Catherine?"

Mark says, "No. I mean he was following her but found her doing nothing out of the ordinary. I don't know what Eddie thought he could find."

Brass sighs and responds, "Eddie was a creep, I'm glad Catherine got away from him when she did. Unfortunately, because of Lindsey she was bound to him for a lot longer. My guess from what you told me is that he was hoping he could pin something on her being a bad mother since he didn't like that the two of you were dating. He tried to pin something like that on her years ago because Catherine missed picking up Lindsey because she was at work."

Mark shakes his head and says, "Well other than following up with Sparky this still doesn't get us any closer to Eddie's killer. I really wish it wouldn't be such an uproar to talk to the undersheriff."

Brass says, "Tell me about it. There's just something about that guy I'm telling you. My gut doesn't usually lie to me about these things."

Mark says, "You know I'm going to give the evidence another look. There's got to be something we didn't find. Actually with the short amount of time there were probably a lot of things we didn't find."

Brass nods and responds, "Ok just be careful, we still need this to be quiet and not raise any questions."

Mark gets up to leave and turns around and admits, "I didn't directly tell Sara but she connected the dots."

Brass chuckles and responds, "You know what bringing her in might not be a bad idea, feel free to work with her."

Mark nods and walks out of Brass' office.

Mark nearly runs into Catherine on the way out.

Catherine says, "Whoa. What's up?"

Mark replies, "Just giving Brass some work to do, you know he never has enough."

Catherine smiles.

Marks turns to leave but Catherine stops him and says, "You look like a man that caught a break, hopefully you can sleep some later."

Mark looks around to make sure no one is around and kisses Catherine.

Once they separate he says, "See you later."

An hour later Mark is in Sara's lab and paged her to join him.

Sara walks in and asks, "What's with the 911 page?"

Mark replies, "Close the door."

Sara closes the door and walks toward the layout table in the center of the room.

Mark says, "I'm re-examining the evidence from Eddie's case and I want to know if you're in."

Sara without thinking about it grabs a pair of gloves and puts them on. They continue to work in silence for a while.

Mark puts some evidence back in the cardboard box and says, "God dammit! Why is this case such a bitch?"

Sara sighs and asks, "What made you open this case again? Was it just because you want to solve it for Catherine?"

Mark replies, "Brass actually approached me with it. The undersheriff apparently has ownership in Sin City Records, Brass thought it might be connected." Mark grabs a file and giving it to Sara and continues, "I made a connection that all of this money was coming out of Eddie's account several times a month and going to one account. Brass knew the account was from a local bank so we went to visit the manager and tracked it to a PI, Sparky Miller."

Sara interrupts, "We've interviewed him several times he's pretty sleazy."

Mark continues, "Well apparently Eddie was paying him but didn't hire him."

Sara holds up her hands and asks, "Wait, what? That makes no sense. Why would Eddie be paying him if he didn't hire him?"

Mark replies, "This is where it gets interesting. Brass pushed Sparky on this one and apparently the undersheriff came to Sparky. Sparky said that he's does work for him from time to time and that the undersheriff wanted him to follow Catherine for a friend."

Sara asks, "Wait our Catherine?"

Mark nods.

Sara sighs and responds, "No wonder you are so conflicted on whether to be a CSI or a boyfriend. So do we know why Eddie was paying Sparky but it was set up by the undersheriff?"

Mark shakes his head and replies, "No. My guess is that with all the smoke Eddie was blowing about my relationship with Catherine he went to McKeen since he was invested in Sin City Records to see if he could find something on Catherine."

Sara says, "This is why you said it was off the record. So I assume Brass suspects McKeen since he closed it so fast?"

Mark nods.

Just then Catherine pokes her head in and says, "Hey I'm heading out. Are you coming?"

Just as Mark goes to open his mouth Sara interrupts, "Cath, Mark is being a huge help to me right now. Do you mind if I borrow him a bit longer?"

Catherine replies, "Oh of course. You two have fun. See you at home."

Just as Catherine leaves Mark mouths a silent thank you to Sara who smiles.

About an hour later Mark is looking at the gun used to murder Eddie under a magnifying scope. Near the serial number there are what appears to be slight abrasions.

Mark requests, "Sara come look at this? Do these look like abrasions to you near the serial number?"

Sara replies, "Yeah. But wait, it's slightly flaky." Sara grabs some adhesive tape and takes a sample and says, "Hodges is long gone I'm going to run these samples while he's not there to scrutinize."

Sara goes to get up but Mark stops her and says, "Sara there's a difference in the metal around the serial number. I think this was tampered with. Maybe that flaky substance is a dried adhesive of some sort. Remember the serial number came back unregistered? Maybe a new serial number was glued over top of it."

Sara raises her eyebrows and states, "It's a hell of a theory. It would definitely open some doors."

Mark sighs and says, "But if I'm wrong it could destroy more evidence."

Sara paces slightly and says, "If it's glued on there we have no choice but to get it off so we can try and run the real serial number. The case is stalled anyways I say risk it what choice do we have?"

Mark grabs a tool and with some work a small metal plate that contained the fake serial number pops off of the gun. Revealing what looks like a bunch of adhesive.

Sara says, "Let's grind it down and apply acid and see what we can reveal."

A while later the real serial number has been revealed.

Mark gives it to Sara and says, "You run it."

Sara types the serial number into the firearm registry and it comes up with a result and says, "Mark call Brass 911."

Mark walks over and sees why Brass needs to be here immediately.

A/N: What did they find out? Who do you think it is? We'll find out soon enough.