[Warning: The below contains MAJOR spoilers for CSI: Vegas Episode 5 “Let the Chips Fall.”]

In the latest episode of CBS’ revival of CSI, Vegas, Gil Grissom (William Petersen) and Sara Sidle (Jorja Fox) think they’ve figured out who’s framed their former colleague David Hodges (Wallace Langham) and may be trying to take down the Crime Lab … only for a major twist at the end.

After tricking IAB’s Nora Cross in Episode 4, Grissom figures out who has the skills to pull this off: Martin Kline (Izzy Diaz), a former medical examiner who has served as an expert witness (like Hodges). He’s the only one who could have fixed a case like Hodges supposedly did. But there’s one problem: He’s not working alone.

Martin confronts Sara and Grissom in the Crime Lab after they’ve started looking into his work, and when he leaves, he tells someone on the phone that they know. By episode’s end, that person has supposedly taken Martin out of the picture: A grenade blew his head off. They ID him by his watch and shoes.

Fox teases what’s next and breaks down that chilling scene in the Crime Lab.

Sara and Gil think they’re making significant progress, identifying Martin Kline, but then he’s killed. How are they feeling after that? Frustrated?

Jorja Fox: Beyond frustrated. It’s almost the end of the line, like they maybe have lost.

Then when Gil looks at the wall in the hallway, he says he thinks the person finally made a mistake. What can you tease about what’s ahead in the investigation and this second person?

There might be one or two more twists ahead. We’re gonna find a person that’s probably going to lead us to another — The stakes have never been higher and the evidence is small. They know they’ve never had less to work with. There’s no support really coming from the Las Vegas infrastructure. They don’t have the credentials they had, and they’re certainly never going to break the law, but they’re really pushed to the limits, not only of their brains — this a very smart criminal — but their access of what they can actually accomplish. Thank God for Maxine Roby [Paula Newsome].

Speaking of, I’ve loved Max and Sara’s relationship from the beginning, how welcoming Max was and everything. And Max is risking her job to let them do this investigation against IAB.

Clearly she’s a mad woman.

Did Sara expect the lab’s new boss to continue to back them as much as she has?

No, I don’t think so at all. And I also think that the last thing that Sara would ever want is to put any additional people in jeopardy. It was a shock, especially through the internal affairs investigation, and really disappointing for Sara to find out that her work was actually not in question. I think she came in guns blazing. She thinks that it’s some of her work, that she signed off on bad police work. And to find out that she was in the clear, but her husband was not, I think really threw her off, but even heightened the stakes even further. So suddenly not only is she fighting for the whole lab’s work, but even her husband’s reputation is personally going to be at risk.

There was something really beautiful about the relationship out of the gate between Sara and Maxine. I think they were both women that had been in the trenches for a long time. And even though they hadn’t met, sometimes in your life, you can look somebody in the eye and you’re just like, “OK, this person understands. They understand.” That was there in the beginning, but I also think Sara does not want to jeopardize Maxine’s place in the lab, nor would she ever want to usurp that authority.

It’s really fun that that Maxine is the boss. That’s been really fun to play. Because Sara hasn’t really been an administrator. I don’t think Sara ever really wanted to run the lab. She liked being in the field, she liked doing the science. Because of the relationship with Gil Grissom, she got a lot of sort of leeway that she might not have had if somebody else had been the boss. And so it’s really fun that that Sara has to work under the confines of somebody else’s rules really for the very first time. Yet the importance of the truth to Maxine and Sara is more important than anything else, in terms of, oh, well, what do your colleagues think of you or maybe even putting your job at risk.

I think so many of us in the world want to do the right thing and when we think about how much we might have to lose, it becomes a really, really, really difficult decision. But I think for Sara and for Max, it’s kind of like, “OK, I’m going to do the right thing, come what may.” They share that, and that’s really fun to watch and fun to play.

Let’s talk about Martin Kline showing up at the Crime Lab. Because the scene was certainly unsettling, but Sara didn’t seem rattled…

The hope was that she was trying to keep her cool and really seemed like she wasn’t freaked out, but yeah, that was an extremely creepy moment, I think maybe one of the scariest in the series for Sara. There’d been times in the past where there have been criminals that had had a personal interest in taking Grissom down and taking Sara down. Sara really almost lost her life once and she almost lost her job a second time. The trick is trying to play it cool, but I think she was shaking in her shoes.

Especially because that lab is so bright, and it was so dark in that scene. I don’t think we’ve seen it like that.

[Laughs] Yeah. It was very, very, very spooky. And that he got in, how did he get in? He got right in, he just showed right up. He’s totally brazen about it. I think it was really great that Grissom showed up when he did. I don’t know if it would have been as polite.