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George Clooney is returning to ER for one episode (Thursday at 10 pm/ET, NBC), but how is it all going to go down? Read on to refresh your memory about his character's past, catch up on current storylines and weigh in on our best guesses for how Dr. Doug Ross makes his reappearance at County General.

Who's Dr. Doug Ross?
Doug Ross (Clooney) is a pediatric-trauma specialist who worked in the emergency room of County General Hospital in Chicago for five seasons on ER. Dr. Ross is a devoted doctor who clearly cares for his young patients — sometimes too much, as his ethically questionable methods often ran afoul of the County General administration.

On the personal front, Ross was initially quite the womanizer, but his on-again, off-again fling with Head Nurse Carol Hathaway (Julianna Margulies) eventually solidified into a steady relationship.

Why did he leave?
The simple answer is that Clooney wanted to leave the show to pursue a movie career. But Ross resigned after he was caught helping a woman euthanize her terminally ill son.

Ross moved to Seattle before learning that Hathaway was pregnant with their twin girls. His departure estranged the couple, as her clinic was shut down in the aftermath of the scandal. Ultimately, though, a year later Hathaway also moved to Seattle to be with Ross, in another top-secret episode in which not even NBC knew that Clooney would appear.

How and why is he back?
Well, we don't know for sure. NBC has kept the details of Clooney's return under tight wraps, so officially we'll all be surprised together. That said, a few details of varying reliability have leaked.

Reportedly (though not confirmed by NBC), former cast members Clooney, Margulies and Eriq La Salle (who played Dr. Peter Benton) and guest star Susan Sarandon all appear in Thursday's episode. In the most recent episode, it's revealed that Dr. Carter (Noah Wyle) has renal failure and is awaiting a donor kidney. In a separate storyline, Dr. Neela Rasgotra (Parminder Nagra) is heading to Seattle to pick up a transplant heart.

In Thursday's episode, Sarandon plays the mother of a boy who is left brain-dead after an accident; Margulies has to break the bad news to her. La Salle bumps into Dr. Carter as he is waiting for his transplant. How all these organs and George Clooney come together is anyone's guess, but if I were to make an educated guess, I'd say Clooney is the brain-dead kid's doctor, and Margulies has a new job working with the organ-donation program. When word gets out of Carter's condition, Dr. Ross and Nurse Hathaway accompany the organs to Chicago, and a tearful reunion ensues.

What do you think? How will the producers weave Doug and Carol back into the storyline?

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