Newly-merged Seattle Grace and Mercy West residents vie for surgeries and their careers, while Arizona stands by Callie when her father employs a priest to convince her to date men, and Izzie experiences the brunt of her new competition.
When you get sick, it starts off with a single infection. One lone nasty intruder. Pretty soon the intruder duplicates. Becomes two. Then those two become four. And those four become eight. Then, before your body knows it, it's under attack. It's an invasion. The question for a doctor is, once the invaders have landed, once they've taken over your body, how the hell do you get rid of them?