By Natalie Abrams
October 15, 2014 at 10:17 PM EDT
Adam Taylor/ABC

The familial relations at Grey Sloan are getting a little twisty on Grey’s Anatomy this season.

In case you’ve gotten a little lost since the show returned, the new head of cardio, Maggie Pierce (Kelly McCreary), is the daughter Ellis Grey (Kate Burton) gave up for adoption, unbeknownst to Richard Webber (James Pickens Jr.), who happens to be the father. That makes Maggie the half-sister to Meredith (Ellen Pompeo) and the half-sister-in-law to Derek (Patrick Dempsey). Sorted? Great, because Meredith has confirmed that Maggie is telling the truth, while Richard finally revealed to Maggie that he’s her father. Say it with me: Drama!

On Thursday’s episode, Meredith will dig deeper into Ellis’ past in a bid to uncover the memories of her mother being pregnant that she seems to have repressed. “I think Meredith feels bad” about getting off on the wrong foot, Pompeo tells EW from the set of the ABC medical drama.

“The status going into the next episode is that Meredith now has confirmation of who she is, but Maggie doesn’t actually know that Meredith has confirmation going,” McCreary adds. “From Maggie’s perspective, it’s probably as icy as they left it at the end of [the second episode]. This is a relationship that is just bad and it’s not going to get better.”

Add that to learning Richard is actually her father, and the overwhelming disappointment leads to Maggie reconsider her job at Grey Sloan. “She’s absolutely in shock because she feels betrayed by this man that she has come to trust, and has really been her one confidante, her one person that she’s been able to connect with on a personal level since she’s been here,” McCreary says. “There aren’t a lot of reasons to want to stay at this point, and there are a lot of reasons for her to go home. At this point, the only reason to stay is to see if there’s any drop of information about Ellis. That might be enough to keep her, but it might not.”

Suffice it to say, Maggie doesn’t plan on giving Richard a chance to explain that even he didn’t know about her existence until her arrival at the end of season 10. “She’s too upset,” McCreary says. “She doesn’t trust him.”

Fortunately, Maggie may find a new ally that could keep her at the hospital. “It’s been a really, really dark road,” McCreary says. “Derek offers a little glimmer of hope.”

Derek may be the bridge between the half-sisters, but that doesn’t mean his fight with Meredith is diminished by any revelations that may come out about Maggie and Meredith’s connection. “He does not find out from Meredith,” Pompeo says. “They’re not talking at the time, so Meredith doesn’t want to engage with him anymore than she has to at the moment. She’s mad at him for the whole D.C. thing still. She doesn’t want to seek out a conversation with Derek about anything, even about that.”

Marital drama aside, there will be plenty of comedy to be had once the news of Maggie’s identity gets out. “Bailey [Chandra Wilson] finds out in a really funny way,” McCreary says. “The information does trickle out and everyone’s reactions are pretty funny.”

Grey’s Anatomy airs Thursdays at 8 p.m. ET on ABC.