Tonight's episode, "What I Am," will feature a number of intriguing story lines as our beloved characters -- and guests -- strive to figure out who they are, what they're made of, and where they're going in life.

Last week, we saw Derek and Finn battle for Meredith's affections. This week, we'll see Derek and Mark (who we know has joined the SGH staff in some capacity) spar professionally as their opinions differ regarding the right course of treatment for a burn victim. Intense.

There's also tension between Cristina (pictured) and Dr. Burke, who she pushes to get better as fast as possible.

The doctors treat a salesman who wants to get back into his routine so he doesn't lose his edge. Addison works with a pregnant woman named Rebecca who may require a C-section (an epidural is not an option, apparently), and the circumstances are such that Mrs. Dr. Shepherd comes to doubt her own skills as a surgeon.

Most intriguingly, as we saw briefly in last week's previews, Meredith has a medical emergency of her own and is apparently worried she's pregnant. Whether that's actually the case or not, we'll have to wait and see.

Then to top it all off, there's the mysterious arrival of guest star Fred Ward (right) who appears out of nowhere to see Izzie, and who we believe plays Denny's father.

Should be exciting! As usual, we'll have our exclusive episode recap up right after the show, and compile our list of quotes, image gallery, and music guide as quickly as we can.

Check back with us often!

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