Tonight's musical event on Grey’s Anatomy is, as Kevin McKidd puts it, the culmination of the season. But there are still a few episodes to go after that. Big ones, too.

“Everything’s in a state of flux…but I think they’re getting down to the nub of what’s going on between Cristina and Owen,” McKidd tells EW of the next few weeks.

“They’ve been pretty content, but they kind of rushed into something without due diligence [regarding] core fundamental things about how they want life to pan out."

"So there are some tough times ahead of them. I think people need to strap in a little bit because it’s going to get pretty bumpy for a while between these two.”

While he stops short of saying exactly how the pair will be challenged, he hints that the duo's longstanding communication issues will play a part in their upcoming troubles.

“I think he gets frustrated because one thing Owen’s pretty good at is that he’s pretty good at expressing how he’s feeling. Sometimes, if she’s in that frame of mind, she’s not that great at reaching out and saying, ‘I need this,’ or ‘I feel this.’"

"I think that is one of his biggest frustrations.”

“I imagine it’s going to raise some pretty interesting debate. Who’s right and who’s wrong. Or is anybody right? It’s definitely going to be an ‘Oh, my God’ type thing. It’s definitely going to be pretty life-changing for them - the final moments of the finale.”

Whether the polarizing debate results in a breakup or a continuation of the happily ever after they signed up for is unclear, but we can't wait to see it play out.

For his part, McKidd says he thinks the pair is meant to be.

“I think Owen and Cristina, from the moment he came out of that ambulance and they met, they were against the odds. When you look at the two on paper, you think, these two shouldn’t be a good fit, and yet they are. When they’re together sparks fly,” he says.

“I don’t think their wedding was their happy ending, but I think eventually - through a lot of make-or-break moments - they’ll end up old and gray together.”

What do you think? Will they? How will the rest of the season unfold for this Grey's Anatomy couple? Share your comments with us below and let us know.

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.