‘CSI’ wraps up its final case Sunday (Sept. 27), with a two-hour movie (CBS, 9 p.m.) that allows one of the most influential and successful shows in TV history to take a well-deserved final bow.

‘If any show ever earned this kind of sendoff, it’s ‘CSI’,’ CBS Entertainment Chairman Nina Tassler said this summer.

The last show, modestly titled ‘Immortality,’ doesn’t only let the CSI team save Las Vegas one final time. It will serve as a kind of memory book, with original lead investigators Gil Grissom (William Peterson) and Catherine Willows (Marg Helgenberger) returning to the fold.

They will join the current team, led for the last four years by D.B. Russell (Ted Danson), to help stop one last batch of ultra-bad guys with the tools of their trade: microscopes, DNA evidence, analytic computer programs and other impressive high-tech stuff.

‘We can’t close every open storyline from 15 years,’ says Jorja Fox, who has played investigator Sara Sidle for the whole run. ‘But the last show is absolutely a love letter to our fans. It’s something I’m pretty sure everyone will enjoy.

‘It’s so unusual in television to get everyone back together like this.’

But then, ‘CSI’ has always been deceptively unusual.

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Real-life forensic scientists have cautioned that some of the techniques and equipment shown on ‘CSI’ are futuristic. Fox suggests its larger premise of scientific analysis is what has resonated with viewers.

‘Forensics has evolved just over the time we’ve been doing the show,’ she notes. ‘Every season we’d get a couple of new gadgets and gizmos. I think one reason we lasted as long as we did was that forensic evaluation felt realistic.’

‘CSI’ didn’t just run on fingernail scrapings, of course. The characters all had their personal dramas, from Grissom’s hearing disorder to his affair with Sara.

‘In 15 years my job never got boring,’ says Fox. ‘There was an arc to Sara’s life, though I never would have seen it when we started. This kind of run is something you never expect, for ‘CSI’ or any other television show.’

The 47-year-old Fox recalls that in the first couple of seasons, ‘CSI’ was considered groundbreaking enough that ‘some people wished we could be on cable, so we could get into more gritty things.’

Looking back, she says she’s fine with the show staying right where it was - and not just because broadcast standards gradually did allow it to show a little more grit.

‘If we were on cable, I’d probably have to be doing some scenes naked,’ she says, laughing. ‘And I’m getting a little long in the tooth for that.’

The return of Grissom in Sunday’s finale does bring Sara and Gus together one more time, which perhaps will help suggest where their characters might head in the future.

Fox says she isn’t sure exactly where that will be, but that after playing Sara for 15 years, ‘I think I probably see her future more clearly than I see my own.’

In the broader picture, ‘CSI’ has simply helped move television police work into a new era.

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In the ‘CSI’ world, the perp could sit sneering somewhere, confident he or she had gotten away with it, while the ‘CSI’ team was painstakingly examining everything this side of dust bunnies to nail him or her anyhow.

‘If ‘CSI’ could just help people understand the value of science,’ says Fox, ’that would be a good thing.’

It’s also not a bad thing that for many years it simultaneously succeeded as television entertainment.

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