Marg Helgenberger wants to unravel her nightmare.

"I was involved in a friend's murder case and I had to explain why I had a bloody shirt on," she says. "The walls were crumbling and closing in on me. I knew I was going to be implicated, so I told myself, 'You better have you ducks in a row!' I woke up very disturbed."

Perhaps fortified by her Emmy-winning tour in the late '80s Vietnam drama China Beach, Helgenberger has managed to hop out of bed and prepare to morph into Catherine Willows, the thick-skinned forensics investigator she pays on CSI: Crime Scene Investigation. Not a lighthearted task, considering CBS's surprise smash--about a crack team of forensics experts who use science to solve murders--is rampant with cannibals, transgendered serial killers and the occasional rotting corpse. Never mind that CSI is set amid the supposed glitz and glamour of Las Vegas: Wayne Newton is nowhere to be found, the suburbs are surprisingly Spielbergian (Poltergeist era), and the Grim Reaper seems to be beating Lady Luck at craps.

Today, Helgenberger, forty-three, and her CSI cohorts are heading to Pasadena to shoot an episode about a woman who's been chomped to bits by her cats. "You have to have a sense of humor around here," says William Petersen, forty-nine, the well regarded film actor (To Live and Die in LA, Cousins) who anchors the show as the confident, enigmatic Gil Grissom, "Otherwise, the gruesomeness gets to you."

All things considered, when it comes to the Case of Helgenberger's Bad Dream, it doesn't take a microscope to see that the show itself could be the culprit. She may get a kick out of taking home bags of flux cat droppings from the prop department to amuse her son Hughie, eleven, but the show, "can be disturbing. I have enormous compassion for the victims, especially when what's happened to them is torn from the headlines, something that really happened. It all infiltrates the subconscious."

She's not alone. Though it premiered in fall 2000 with slightly more fanfare than a late-night informercial, CSI has seeped into the nation's psyche like no other show since Fox's The X-Files. Initially positioned Fridays at 9 p.m. (a la X-Files), the series was expected to reap just a bit of the bonanza from The Fugitive, the retread of the '60s thriller that CBS and critics pegged as one of the hits of the season. Compared to sleek-as-Helgenberger's coif CSI , The Fugitive looked fuddy-duddy and fizzled. Meanwhile, the show about people running to death nabbed more than 17 million viewers in its debut.

Suddenly CBS, home of aging shows like Touched by an Angel and JAG, had a series that, unlike Wolf Lake, was edgy but mainstream friendly. A bit of an anomaly that combines old-school storytelling and characters with ha-cha-cha cinematic flourishes like ingenious camera angles, and eerie postcard shots, CSI offered the net the perfect demo marriage gift: something old, something new, something borrowed, something -- well -- blue.

After CSIs go-for-broke move to Thurdays last season opposite NBC's Will and Grace and Just Shoot Me, the mix proved even more potent; there, CSI had a powerful Survivor lead-in and kept growing. Earlier this year, the show made it all the way to No. 1, topping even a fresh episode of ER. And critics have even taken to the gruesome pop. "A hip show on CBS?" gushed Vanity Fair's normally non-gushy James Wolcott. He gave it four stars.

"Its like we won the lottery," says a still-blown-away Helgenberger, who credits the success to "many elements--the fantastic crew, the producers, the cast." And don't forget O.J. Simpson. Most here believe the murder trial of the former football star--and America's resulting fascination with DNA samples and the like--paved the way for the show's success. "Everyone was intrigued by those bloody gloves," say the actress. "And here we show how the pieces come together." Adds Petersen, "Forensics can help even more than confessions, which can be thrown out. You can't argue with science."

It took show creator Anthony Zuiker to see the potential of melding that science with fiction. Zuiker, a brash, big-hearted Vegas guy who drove a tram at the Mirage hotel before taking a stab at writing, was a fan of the Discovery Channel's reality forensics foray, The New Detectives. Adding his own experience--when he wasn't steering tourists, Zuiker indulged in scary rides with a buddy in the police department and later befriended forensics investigators--he whipped up some notes and pitched the show to movie king Jerry Bruckheimer (Black Hawk Down).

A jazzed Bruckheimer took it to ABC, promising a sleek-looking show that would echo his flicks. After the Alphabet passed (fearing it was too expensive), CBS senior drama veep Nina Tassler jumped on it. Just one snag: time to make the fall sked was running out. In quick order, network president Les Moonves went to Peter Sussman of Alliance Atlantis. Sussman and cochief Ed Gernon--whose company was know mainly for producing TV movies and minis like Joan of Arc -- were confident their outfit could make its mark with the show.

But whom to cast as Grissom? The net had long been looking for a project for Petersen, who, despite a sharp turn in the recent political drama The Contender, had grown increasingly bored with features. "The business had changed, and I didn't want to make movies that I would not see myself," says the Chicago native, a onetime high school jock who admires "electric" types like John Barrymore and Marlon Brando. TV-ready as he was, "I didn't want to play a doctor, a divorce dad, lawyer, or cop. So I was turning down a lot of stuff." When CSI came along, he saw a trace of the title character he'd played in director Michael Mann's 1986 cult hit Manhunter, about a profiler haunted by a serial killer. Grissom, he says, "was someone I understood."

Petersen was given a heady match in Nebraska-raised Helgenberger, who lends a Midwest cynicism to her part as single mom Catherine While it was recently revealed that Catherine was an exotic dancer long before joining the CSI team, that doesn't mean she's playing an extension of K.C., the hooker she played in China Beach.

"K.C. was a recluse out to make a buck, but Catherine is more open. She's out to make a difference," says Helgenberger who, after sighing that movies like Species were taking her away too much from her family, was urged by her agent to consider CSI. "And he was absolutely right. After reading the pilot's first draft, I could see that the show was innovative and provocative, had incredible attention to detail, and I like that it was laced with black humor. So I went after it."

With the two leads set, casting centered on a trio of supporting characters, a veritable neo-Mod Squad of sexy, edgy forensics flunkies. As criminalist Sara Sidle, Jorja Fox, thirty-three, a bohemian type whose backstory includes recurring roles on ER and West Wing, would be the neo-Peggy Lipton. Gary Dourdan, thirty-five, a Meisner-trained Philly native who got his start on A Different World, landed the part of sly Warrick Brown; in Pleather jackets, "War" looks as groovy as Linc. And Savannah's George Eads, also thirty-five and a former public relations major from Texas who could pass for a navy S.E.A.L. (or a crew-cut Michael Cole), completed the triangle as hot-shot Nick Stokes.

Also in the mix; quip-handy Eric Szmanda, twenty-six, a former alterna-rock promoter who plays forensics' geeky analyst Greg Sanders, and classically trained Robert David Hall (coroner Dr. Robins). Hall, the warm-hearted statesman of the bunch, lost the use of his legs twenty-three years ago--the result of an accident with a drunk driver--and is one of the industry's best-known disabled working actors. People with disabilities "are thrilled to have someone on the number-one show," Hall says.

The CSI-ers have quickly become TV's hottest heroes. Noble but flawed--hey, it takes a dark perspective to deal with stalkers and brains in pickle jars--Grissom and gang are the archetypal comic-book goods guys, who despite lacking supernatural powers, are more X-Men than X-Files. Just when things look dour, elements of day-saving Quincy and Kojak pop up. "We're all TV babies," says Petersen , who as a kid spent Saturday afternoons watching Charlie Chan flicks on the tube. "So it's fun to be in a show that's kind of a throwback."

And in a show where everyone seems to get along, "I've never felt closer to a group of people," says Fox--a good thing, since the group is usually exiled to quiet Santa Clarita, a residential town one hour north of L.A. that pinch-hits for the Vegas suburbs. "It's a long haul," Helgenberger says. "There are lots of graveyard shifts and night exteriors. Everyone gets fried."

Keeping them going through the twelve- to fourteen-hour days is Petersen. Helgenberger--who's got the skinny on her castmates--duds him "the quarterback" (during football season the gang heads to his Hancock Park house most Sundays to catch NFL games). "Sensitive poet" Dourdan leads the cast in guitar jam sessions. The single Eads is the "little brother" who likes to hit L.A. hotspots like Three Clubs.

Fox, a Florida beach girl, is the "cool-but-sweet chick" who surfs and downs veggie burgers. And "I'm the mother hen, for sure," says Helgenberger She's even been known to bring in pies for the cast and crew. "I'm no Betty Crocker, so I don't actually make them," she laughs. "I just try to make sure everyone's doing okay, keep the spirits up."

Also helping are perks like "great Dodgers tickets," laughs Petersen, who is also a producer on the series. A bigger source of motivation is the realization the CSI offers "an oddly communal project," adds the actor. Unlike a David E. Kelly or Aaron Sorkin series, CSI "isn't essentially the voice of one person," he says. "Everyone is able to contribute." Which is great, adds Eads: "We all really care about what we do."

And it shows. Earlier this year the cast was nominated for the SAG Award for best ensemble in a drama series, alongside the stars of Law and Order, The Sopranos, West Wing, and Six Feet Under. Also giddy-making: the likes of Kevin Spacey and Carlos Santana have cornered the cast with raves at awards shows. While the quick attention may sound like a breeding ground for plump egos, so far things are in check. Dourdan, the show's resident rising hunk, "gets mobbed the most intensely," says Fox. "But he's grounded. Everbody's very grounded, even though we feel like we're riding the tail of a comet sometimes."

It's not the fame but the work that Eads admits he takes too seriously sometimes. One recent day on the set, "I wasn't believing what was happening to my character, and I expressed my frustration. Marg finally said, 'Hey, man, we're number one! Have fun.' She laughed, and I thanked her for putting things in perspective."

It helps that everyone seems to acknowledge that the true star here is science. Plots are well researched and often based in sad, true cases like child abductions; and bandied-about references to electrothermal atomizers and ulnar loops aren't just mumbo jumbo. In fact, the biggest acting challenges on CSI include "holding up hair fibers so that the camera picks it up," says Petersen, "and pronouncing the chemistry terms well enough that the audience believes you." For help, the cast turns to tech adviser and story editor Elizabeth Devine, who slogged for fifteen years with the L.A. County Sheriff's Department. The show also gets some of its netherworld reality from Jerry Stahl, the former Moonlighting writer who later detailed his bout with heroin addiction in the book Permanent Midnight.

Beyond the public's seeming yen for vigorously checked blood splatters, can CSI success be attributed to something, like a bit incriminating cotton, that we're not seeing? Consider: HBO's acclaimed Six Feet Under also opens each episode with an icky demise "There is, of course, a fascination with death out there," says Petersen, who for the record believes in the afterlife. "People are interested in what happens to them after they're gone, and on one level, this show touches on that fantasy. But we don't analyze it too much." Though one April episode featured a clairvoyant, a book popular with writers set the tone: Practical Homicide Investigations anyone?

Still, the musing Petersen, who's prone to passing out T-shirts emblazoned THINK, notes that the show's theme song -- Pete Townsend's "Who Are You?" -- has "several connotations. It doesn't' just refer to victims or perpetrators. It's also about, 'Who are we, and who are you?'" While Grissom himself has been known to spout off about Maslow's hierarchy of needs, viewers looking for any more philosophizing can hit the self-help section. "CSI is pure, self-contained mystery with a satisfying resolution," says Petersen. Denouement, not death, is the bigger draw. "There's closure, and that comforts people these days."

Lots of people. CSI is also a phenomenon in Europe. In the U.K., it has put Channel 5 on the map. CSI mania is so rampant in England that plans are afoot to take the cast there later this year. Back home, TNN will start airing CSI this fall in a $1.6 million-per-episode deal. The show has also inspired a rash of flatterers, from NBC's Crossing Jordan to a Fox forensics reality show (airing suspiciously, on Thursdays before CSI) to the ABC pilot EIS, which hopes to mine intrigue from the Centers for Disease Control. And CBS would be remiss without turning its own smash into a Law and Order-like franchise. CSI: Miami, featuring a completely different cast headed by David Caruso, is already up and running to the fall slate.

"We're in our groove," says Petersen, who's also happy in love (he plans to marry his theatre-world sweetheart, Gina Cirone, next year in Italy). Still, getting the show to the point where everyone's happy" hasn't been an easy process," says the patient Dourdan, who hopes to direct some episodes. Character development is one priority. The first season's episodes didn't reveal much about the characters' private lives, but the audience has lately been teased with a bit of background here and a budding romance there (Sidle seems to have a crush on the detached Grissom). It's all CSI game. "What really hooks you," says Eads, is that you don't know too much about these people. So when the nuggets come, they're gooooood."

Helgenberger, for one, hopes her character gets one of those nuggets soon. "I'd really love to explore some things," says the star, fully recovered from that bad dream. "Like, just how did Catherine get to be an exotic dancer?"

In CSI the physical evidence of a crime often takes on the role of a character, and the way that character"talks" is bringining something new to TV narrative techniques.

INserts that have come to be known as the "CSI shot" use computer graphicsd and animation to explain often obscure scientific principles and the role they play in solving crimes. In every xript, the shot provides exposition so quickly and painlessly that most of the audience never notices.

It's anew answer to an old problem. Viewers need to know enough to understand the story, but complicated expostion can turn the snappiest script into a bog of boredom.

"We wanted to psuch the envelop for visual style, but we also wanted to incorporate that information in a way that wasnt going to slow down the action," says creator-executive producer Anthony Zuiker. "That meant briniging the special effects and postporduction crew into the process far earlier than is normally done.

"It's noit enought to just put down a dexription on the page of what you want to see. We look for excuses to use visuals (as expositoin) rather than talking heads.. Bujt getting from the page to the scerren demands that we collaborate early and often with the people doing that work. For instance, the writer may (envision) something like green pancake batter hitting the lens and then becoming something green with a thumbprint in it, but has no idea of exactlyhow that;'s going to be rendered.

"Ww have writers who have a background in forensic science, but ralizing their fvision accurately and coimpletely requires collaboration. (The procesd) srarts in the writing room when we are ceating the story line, and then the writer shepherds it through the visual effects process. It's not just handing (the technicians) the written page, but also haveing a dialogue with them. Our writing team has been expadned to incude the SFX staff."

Other shows, notably the various Star Trek series, also enjoys a close collaboration betweeen the writers nad SFX/pstproductin. What distinguishes the CSI shot is the way computer graphics and animation are blended with voice=over and sound effects to give the audience essential informatoin. Thle shots are used to demonstrate the path that a bullet took throogh a victim's body, while avoiding the confusion and gore of the real thingl. They mayh re-create a bujs crash without the visual confusion or blood splatters. The show also makes extensive use of sna-zoom transitoins and montage shots to aid the narrative, often in conjuecniton with the CSI shot.

"Our intent is to keep the audience on the same page as tjhe investigators," says associat p[roducer Brad Tanenbaum. (We need to: explain what the bullet does when it strikes somebone's body. WE show and tell at the same time. Macro-photography, computer graphics and motion control techniques are all used, as is prosthetic makup by out colleague John Goodwin, who makes us very realistic body parts."

Tanenbaum pauses and reflects. "It's rather better than trying to work with the real thin," he deadpans.

Tanenbaum and his colleagues - coproduce Bruce Golin and Larry Detwiler, visual effects superviosr at L.A.'s Stargate Digital, wshere all CSI special evvects are done--agree that being involved while the script is developed gives them more creative range.

"It's hard to be originla on television," says Detwiler, "But htere are some things in this show that I've never seein in my twseny years in the busniness."

==Francis Hamit