Grey's Anatomy Sneak Peek: Derek's 'Killer' Sends Meredith Running

On the occasion of its 250th episode this Thursday (8/7c on ABC), Grey’s Anatomy is throwing the dinner party from hell — and we’re all invited!

The milestone outing picks up right where last week’s episode left off, with Meredith discovering that Callie’s new mystery girlfriend is the incompetent MD who failed to save Derek’s life. And this walking painful reminder, Penny, is now inside her house snacking on her hors d’ oeuvres.

As you can see via the video sneak peek above, Mer initially resumes her hostess duties, as if to say, “No worries, universe — I got this!” But then she spies a framed photo of Derek out of the corner of her eye and promptly goes into extra dark and twisty mode.

Press PLAY above for a first look at “Guess Who’s Coming to Dinner?,” then hit the comments with your thoughts/predictions. Also, there have been 250 episodes of Grey’s Anatomy, people. That’s nuts, right?