Ellen Pompeo and Patrick Dempsey

Patrick Dempsey is riding a uni­cycle. It's 10 o'clock on a Wednesday morning, and the Grey's Anatomy leading man is playfully entertaining the cast and crew between scenes at a downtown Los Angeles theater complex. Long before Dempsey stepped into Derek Shepherd's sexy scrubs, he was (hidden-talent alert!) a champion juggler and avid student of the circus arts, and it's clear as he pedals around the set clad in a black tux that he's still got serious skills. "I'm tired of being an international superstar," he cracks. "I'm running away to join the circus!"

No need: The circus has come to him. Scattered among the dozens of formally dressed extras in today's party scene — an over-the-top fund-raiser for Grey Sloan Memorial that Jackson (Jesse Williams) has organized to benefit the superstorm-­ravaged Seattle hospital — is a plethora of colorful performers, including a fire-breather, a brave soul on sky-high stilts, a tightrope walker and several eye-poppingly flexible contortionists. "Jackson thinks it's going to be a very tasteful, elegant gala," says executive producer Shonda Rhimes, "and instead it turns out to be a hot mess."

Off screen, the celebratory spectacle feels appropriate: After all, it's not every day that a network series hits the 200-episode milestone, ­especially in today's fractured, übercompetitive TV landscape. It's rarer still that a medical drama in its 10th season should still have such a strong ratings pulse. Grey's Anatomy currently ranks as ABC's No. 1 drama among the advertiser-coveted demographic of adults 18 to 49 and remains a Top 20 drama among total viewers.

In honor of the landmark occasion, Rhimes set out to craft an episode that, she says, "rewards viewers who have watched the show from the beginning in a way that's special." That means a throwback to the hyper­competitive spirit Meredith ­ (Ellen Pompeo) and her best friend, Cristina (Sandra Oh), exhibited as surgical interns in the drama's early days, a fire that's reignited when they learn that the gala's top fund-raiser will get a cut of the cash for his or her own hospital department. Hence, a cocky Cristina plies a donor with copious amounts of alcohol, Meredith works the room in a sexy Gucci gown, and Callie (Sara Ramirez) milks sympathy by telling what Rhimes describes as "a pretty horrible lie about her relationship" with estranged wife Arizona (Jessica Capshaw), who cheated on her in last season's finale.

The episode also features huge turning points for several characters, including the show's central couple, who have been on leave from the ­hospital since the birth of their son. "Derek and Meredith have a pact that if she can't work, then he can't, either," Pompeo says. "But they're going crazy because they're not doing surgeries, so they kind of cheat." And since a gala "is not a Grey's gala if somebody doesn't get hurt," Rhimes teases, "Meredith sees the opportunity to jump into an OR, and she takes it."

In addition, Rhimes says the Chief (James Pickens Jr.), still hospitalized after his storm-induced electrocution, "finds the will to live," and on-off couple Cristina and Owen (Kevin McKidd) "are both seeing what else is out there. I don't know that Cristina's 100 percent ready, but for Owen, the results are surprising."

It's Alex (Justin Chambers) — finally stable and happy, thanks to his relationship with Jo (Camilla Luddington) — however, who gets the biggest shock, when his estranged junkie dad (Dexter's James Remar, beginning a multi­episode arc) suddenly appears early in the season. "It's very emo­tional," Rhimes says. "It's a chance for Alex to figure out who he is as a man."

Adds Chambers, "The next few episodes are kind of heavy for Alex, but Jo's going to help him through it." Or maybe not. "If there's one thing I've learned on this show," he adds with a laugh, "it's that things can change on a dime!"

For more on Grey's Anatomy, pick up this week's issue of TV Guide Magazine, on newsstands Thursday, Oct. 3!

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