On last week's episode of "Grey's Anatomy," recently-widowed Meredith (Ellen Pompeo) came face-to-face with an unwelcome reminder of Derek's (Patrick Dempsey) death: The doctor whose bungled medical care killed him, and who also just so happens to be Callie's (Sara Ramirez) new girlfriend, Penny (Samantha Sloyan).

This awkward meeting plays out throughout the series's next installment, set to air on Thursday, when Callie brings Penny to a party at Meredith's house. Meredith, realizing who Penny is, rushes upstairs, clutching a photo of her late husband.

As she paces around her daughter's room, reminders of Derek everywhere (including their marriage Post-it), Meredith flashes back to the awful day that Derek died, and her last conversation with Penny, when the tearful doctor apologizes for her lack of skill. In the present, Meredith hyperventilates, dreading returning to the party.

The scene is part of the show's landmark 250th (!!) episode, which will also feature Arizona's (Jessica Capshaw) nervous first meeting with her ex's new GF. Check it out below. "Grey's Anatomy" airs Thursdays at 8 p.m. on ABC.