Callie and Meredith will get into an argument over Penny in the upcoming episode of "Grey's Anatomy" entitled "Something Against You."

A promo for Thursday's episode showed Callie asking Meredith why Penny isn't being treated like the other residents. She also tells Meredith that Penny should be given a chance to learn and that she should be with them when they do the skull transplant.

But Meredith isn't convinced, and she says she wants Penny to be with the donor.

"What for? Why are you doing this? What, do you just want her to sit there and think about what happened to Derek?" asks Callie.

An embarrassed Penny asks her girlfriend not to interfere, and Callie leaves in a huff. But Penny isn't done with Meredith.

"I'm here to learn. I want to learn, but you have to teach me," Penny says in the promo. "Treat me like any other resident—treat me worse, I don't care. Hate me, yell at me, I can handle it!"

Callie's new girlfriend also reminds Meredith that it was she who told her not to quit.

"If you can't do what you are here to do, then please let me go," says Penny.

Elsewhere in the episode, we'll see Owen butting heads with Martin Henderson's Nathan Riggs, who came to Grey Sloan Memorial Hospital in the previous episode. It looks like Nathan will be one of the new doctors joining the hospital, and Owen isn't pleased with this new addition.

As the episode progresses, we'll learn more about Nathan's past and find out why Owen hates him so much.

"Grey's Anatomy" is aired Thursdays on ABC. Click here to watch the episode online.

The official synopsis for "Something Against You" reads:

The team of doctors work on a high stakes case of a long time patient, adding additional pressure to an already tense environment. Meanwhile, Bailey wants Ben to kick out their new roommate, and Arizona is eager to get back into the dating world with a new wingman.