How do you follow up one of the biggest ratings smashes of this century? If you’re “CSI” series veteran Jorja Fox, you do it carefully. Six years after “CSI: Crime Scene Investigation” wrapped up its massively successful, 15-season run on CBS, Fox’s character, Sara Sidle — and her longtime co-worker (and romantic interest) Gus Grissom (William Petersen) — will be returning to Sin City for CBS’ new 10-episode event series “CSI: Vegas.”

Originally commissioned for the 20th anniversary of “CSI: Crime Scene Investigation” in 2020, Deadline reported that the pandemic delayed filming on “CSI: Vegas” and led to it getting pushed back a year. The new title is an indication of how much the world has changed since 2000. Two decades ago, a lot more people needed help in order to know what “CSI” stands for, while in 2021, even the returning mothership has to be distinguished from its three different spin-offs, much as “Star Wars” picked up the “A New Hope” appellation in 1981.

Fox’s tenure on the original series was complicated, but she was there for the series’ beginning and for its end, which makes her well-qualified to judge what might make a sequel a worthy endeavor. Now that “CSI: Vegas” is finally set to premiere in early October, the actress spoke with the Las Vegas Review-Journal about why she decided to return to Las Vegas, and what fans can expect from Sara Sidle in the new series.

For one thing, the decision to come back was complicated by where Sara ended the show, and how pleased the actress was with her resolution, which saw her reunite with Grissom to sail off into the sunset. Fox said she felt it was a blessing that the show was able to go out on its own terms when it ended in 2015, providing the sorts of resolutions that you can’t get when cancellation catches you by surprise. Since Petersen, who left the series during Season 9, returned for the two-part finale, the pair’s relationship was able to achieve closure. “I was really, really happy where Sara and Grissom were left,” she told the Review-Journal.

And so when she was approached about coming back for the limited series, there was only one way Fox was going to agree to do it. “It was important to me that if Sara was going to come back, I really wanted her to come back with Grissom. You know, they were together and not together, and married and broken up, and taking time apart and living apart. For it to really work, at least storywise for me, then I really wanted it to be both of them.”

She got her wish. Petersen returned, as well, and “CSI: Vegas” sees the pair of them a little more secure in their relationship, which Fox said was fun to play after years of ups and downs. The new series once again requires them to come together professionally. The series’ trailer hints that something happens that calls hundreds of results delivered by their lab into question, meaning any defendant put away with their help might get a chance to go free. The pair, the Review Journal says, return to Las Vegas to protect the integrity of their work.

While they struggle to hold together years of prior cases, a new generation of forensics experts will be solving new cases. Led by Maxine Roby (Paula Newsome), the new team will take advantage of a variety of breakthroughs made in the science of forensics over the last two decades to solve new crimes (just maybe don’t take the show’s word as gospel when it comes to the science or procedure.) In addition to Fox and Petersen, Wallace Langham returns as lab tech David Hodges, while Paul Guilfoyle makes a guest appearance reprising his role as Jim Brass from “CSI: Crime Scene Investigations.”