This Thursday's episode of "Grey's Anatomy", which is the mid-season finale, will probably shed light on what went between Owen and Nathan that resulted in Owen hating the new doctor so much.

The mid-season finale episode, titled "Things We Lost in the Fire", doesn't reveal much about what went down between the two. But in a recent interview with Entertainment Weekly, Kevin McKidd, the actor who plays Owen, said that it has something to do with life and death.

"All I'll say is it's life and death. It's a life and death thing," McKidd said. "He's not ready to talk about it, but something obviously dreadful and awful has happened between he and Riggs. We will find that out. I can't tell you what that is, because that would spoil it. But it really triggers a lot of that dark[ness]."

Besides Owen and Nathan's mysterious past, the viewers might also see something monumental happening between Jo and Alex. It looks like Alex's over-involvement in Meredith's life is going to rub Jo the wrong way.

Jo is in a precarious position, especially now that Stephanie has put the doubt in her regarding her capabilities as a surgeon. Added to that, Meredith's apparent disregard for Jo isn't helping matters much.

In the promo for Thursday's episode, Jo complains to Alex that Meredith treats her like a stray dog.

"You know when I had a minute? This morning when you and Meredith were whispering in the hallway and she yelled 'Get away' in my face like I was a stray dog," Jo tells Alex.

When Alex bursts out laughing, Jo snaps that it isn't funny.

"That's not what she meant," Alex tries to defend Meredith.

"God, you always defend her even when she's being a complete b*tch to me," Jo fires back. "Don't do that. Don't call her that...," Alex warns his girlfriend.

The official synopsis for "Things We Lost in the Fire" reads:

As the rumor mill around the hospital continues to spiral out of control, Grey Sloan Memorial is flooded with injured firefighters from a nearby wildfire. Maggie struggles to keep things with Andrew professional at work. Meanwhile, Jo questions Alex's priorities.

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