The next installment of "Grey's Anatomy" season 12 will see a painful part of the past continue to creep back in. As Meredith, and the whole fanbase, struggle to move on from the death of McDreamy, the person responsible for saving the life of the surgeon shows up right at Meredith's door.

In fact, this person, whose name is Penny, was introduced by Callie as her new girlfriend. In the episode, which is titled "Guess Who's Coming to Dinner," viewers will get to know more about her and how her arrival shakes up the whole dining table.

The promo for the "Grey's Anatomy" season 12 episode shows Penny admitting that it was her job to save Derek but failed. It has continued to haunt her and had her thinking ever since that she was not good enough of a doctor to save him. But being a doctor herself, Meredith understands Penny.

Although she is shocked and uneasy about having a meal with the person that had the means to save her husband but still couldn't, Meredith was composed enough to tell Penny that she just has to be better instead.

The impact of Penny's arrival hits more than just Meredith. Arizona, who is also at the dinner party, gets to officially meet and even dine with her ex's new girl in this week's "Grey's Anatomy" season 12 installment. Needless to say, Arizona is anxious to get to know more about her.

The episode will also see Maggie, who was supposed to prepare the dinner for their friends, rush to the hospital to deal with an "embarrassing issue" that likely has something to do with her hook-up with intern Andrew.

With no one to cook, April helps out in the kitchen not only to make sure there will be good food to serve but also to avoid Jackson, who is also present at the get-together.

Indeed, there will be a lot of awkwardness and intense scenes in "Grey's Anatomy" season 12 episode 5 titled "Guess Who's Coming to Dinner" when it airs on Oct. 22 on ABC.