Marg Helgenberger, left, hugs Capt. Jim Brass as other CSI...

Marg Helgenberger, left, hugs Capt. Jim Brass as other CSI members including Ted Danson, left, Jorja Fox and Eric Szmanda look on in her last episode on "CSI: Crime Scene Investigation" "Willows in the Wind." Credit: CBS

Last week, three employees of a law firm were shot in cold blood, and their bodies disposed of -- only to be consumed by genetically engineered bugs that could down a Big Mac in less time than it would take a person to eat one. This Wednesday, it won't be giving away too much to say that people die, and those ravenous bugs get another close-up. But the big news is this: Catherine Willows, who has been on virtually every episode of the most successful TV drama of the past decade, leaves. (We won't say how -- that would be giving away too much.)

Over the years, Catherine hardened: Those dark enigmatic eyes narrowed, while the cynicism -- and glam -- grew along with the gorgeous locks. Then almost before anyone knew it, Willows -- and Helgenberger -- became the bedrock of this classic series, as commanding a presence as few actresses have ever been on a cop procedural.

Helgenberger gave a show about (let's face it) cadaver dissection allure, mystery and, above all, sex appeal. She put the "noir" in "CSI," and in fact would have been a terrific noir actress 65 years ago -- a Veronica Lake, Ida Lupino or, on her best days, Lauren Bacall. We all know the old truism, "Everyone's replaceable," but Helgenberger on "CSI" may be the exception.

(Elisabeth Shue joins the cast Feb. 15 as Julie Finlay, an investigator fresh from an anger-management course who also shares a past with Ted Danson's D.B. Russell.)

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