After 15 seasons of riveting medical drama, merry-go-round romances and startling plot twists the "ER" era comes to an end. But the road to "ER's" final sendoff should be a nail-biter.

Producers tossed plenty of bones out earlier this season to hook diehards. The return of original cast members as Anthony Edwards, William H. Macy and Noah Wyle sent hearts fluttering - no defibrillators needed here.

That parade of "ER" alumni clearly signalled what producers were up to: The inevitable, riveting resolution of this hit's old, intertwining story lines.

March 12th's episode boasts the return of Eriq La Salle, who as Peter Benton, will visit the ailing Dr. Carter (Wyle) as he waits for a kidney transplant.

Hollywood movie stars Susan Sarandon and George Clooney also fill out "ER's" dance card.

Sarandon joins "ER's" March 12 episode as a grandmother of an ailing patient.

Clooney and Julianna Margulies (old flames Doug and Carol) could deliver the romantic reunion of the year in Thursday's show. Margulies has admitted she and Clooney returned to the set for two days of quiet filming, but they agreed to do it with the promise of no PR hype.

Now one of the most powerful men in Hollywood, Clooney's career soared after he donned "ER's" scrubs and started playing doctor with nurses in County General's linen closets.

Margulies left the show in 2000. (Clooney returned for a cameo at the end of her last episode.) She went on to appear in TV shows like "The Sopranos" and "Canterbury's Law."

Both actors scoffed at rumours about a possible "ER" reunion earlier in 2009. Clooney's publicist said "It's something he has already done."

Margulies told the press, "I left Carol Hathaway in the best scenario possible. I can't imagine making it any better."

"ER's" writers, however, didn't feel the same.

Producers still remain mum about what transpires between Doug and Carol. In February of 2009 Margulies told the press that satisfaction rather than sensationalism would define their reunion. Viewers would "pick up a slice of their life now."

True though that may be, expect tears -- and the hospital's body count -- to somehow multiply once Doug and Carol say their final farewells.

TV's former "Gilmore" girl, Alexis Bledel, guest stars on the two-hour series finale, airing April 2.

As Dr. Julia Wise, Bledel will trade in her "Travelling Pants" for the scrubs of a new intern at Chicago's County General.

Little else remains known at this time about "ER's" finale. But it, like all the other episodes before it, should remind fans of one thing: Great storytelling like this lives on, even if "ER" doesn't.