'CSI's' 300th episode...tonight

"CSI" has arrived at three hundred episodes, and to put this milestone in some perspective, only eight other network primetime dramas have hit that threshold, (including "Law & Order: SVU.") Marg Helgenberger returns for this one, and if you head to the jump, two little elements - CBS's most recent promotion for tonight's Big 300, and my piece from today's Newsday on What It All Means. And as usual, Newsday app readers please head to newsday.com/tvzone to watch the clip, especially if you want to hear the correct pronunciation of "Marg"...

THE SHOW "CSI: Crime Scene Investigation" WHEN|WHERE Wednesday night at 10 on CBS/2

WHAT IT'S ABOUT For Wednesday night's 300th episode, Marg Helgenberger returns for a one-night-only appearance to help in a 14-year-old cold case about a onetime casino executive who was squeezed for a similar crime all those years ago. Expect flashbacks -- hey, what was the gang doing way back then, and -- more important -- what was Catherine Willows' hairstyle? Also, expect maybe a surprise or two? (No review screener was available.) MORE: Latest TV coverage | Reality TV | TV Zone blog | TV Listings

MY SAY Hard to tell how seriously even "CSI" takes itself anymore. Last week, for example, began with a contestant on a cooking reality show who disgorged an eyeball, with the camera lovingly capturing its trajectory across the floor. Naturally, the eyeball was a human one -- a fricasseed specimen, complete with a contact lens.

"CSI" has always had a morbid sense of humor, possibly a writers'-room defense mechanism against staleness -- or insanity. Either one might easily come with this kind of territory after 300 episodes. Only eight other prime-time dramas in TV history have exceeded 300, three of those on CBS, none of them (with the possible exception of "Gunsmoke") approaching the body count.

But great serial franchises don't endure on blood and eyeballs alone, no matter how imaginatively rendered, but on great characters. They have been here in abundance, although only two have truly stood out over the years. William Petersen's Grissom left in 2009, and as perfectly adequate a replacement as Ted Danson's D.B. Russell has been, he is no Gil.

Eccentric, and emotionally disengaged, Gil was also a practicing entomomaniac. Yes, that's a real word -- someone who is unusually passionate about insects -- and needless to say, Gil was TV's first.

The other one returns Wednesday night -- Willows left after the 12th episode of the 12th season, and took with her a backstory even nuttier than Grissom's. But when she left, so did most of "CSI's" exotic allure. As good as Elisabeth Shue's Finn is, she's much more like a soccer mom than a splatter specialist. Willows was all shadows; Finn is all light.

And so, Willows returns for a brief reminder of the golden years, when "CSI" was TV's most-watched scripted series (2002-07), and No. 1 show (the 2002-03 season) -- and no one then did anything as loony as spitting out eyeballs to get attention.