Grey's Anatomy Episode Stills: "Invest in Love"

Promotional photos from this week's episode of Grey's Anatomy, "Invest in Love," show the gang in a festive mood. Or are they? Arizona is under a lot of pressure to save a patient.

Yes, that's always the case for a doctor. But one of this patient's parents has a donation of $25 million Seattle Grace may be able to garner. You can imagine how the Chief reacts.

Arizona, along with girlfriend Callie, is front and center in many of the photos below, as are Mark and Lexie. What a cute couple they make. What do you think they're celebrating? 

Click to enlarge the images below and tell us what you think...