This week on "Grey's Anatomy," Meredith will be reminded once again of Derek's death when someone from the past shows up at her dinner party.

In the sneak peek for the episode titled "Guess Who's Coming to Dinner," the scene picks up where it left off last week, at Meredith, Maggie, and Amelia's dinner party. Callie arrives with her new girlfriend, Penny, who happens to be one of the doctors who couldn't save Derek's life. Meredith recognizes her and is reminded of Derek's death, and she tries to shake it off while everyone else in the house introduced themselves to Penny.

April goes to Penny to introduce herself, and Meredith watches the interaction with a pained look on her face as she keeps her hands on top of a blender.

"Kepner's on trauma," Callie tells Penny as April walks away. Callie tries to explain April's situation with Jackson, as she continues, "Her husband is on plastics, although, maybe not her husband…We don't know. They might not know." She adds that Jackson's family owns the place, but reassures her that it's "not nepotism, he's great."

"At last, we get to meet the legendary Penny!" Amelia exclaims while handing the newcomer a drink. "Whatever she tells you about us, just ignore it," she quips while giving Penny a hug, much to Penny's mingled surprise and pleasure at her warm welcome.

Penny appears to notice Meredith staring at her as she furtively glances at Meredith while Amelia is talking to her and Callie.

"Amelia's chief of neuro…a little volatile, but outstanding," Callie whispers to her new girlfriend.

Alex notices that something is amiss with Meredith, as he gets her to turn off the blender and he asks her what's going on. Meredith replies that she's great, but Alex seems to think otherwise.

"You're not great, you're freaked out, you're smiling a lot," he points out. Alex added that Meredith is acting as if she's in a hostage video and insists that something is wrong.

Meredith is at a loss for words, and on Thursday, viewers will get to see whether she'll tell everyone how she knows Penny's girlfriend and the circumstances that led to their initial meeting.

"Grey's Anatomy" airs on Thursdays at 8 p.m. on ABC.