Nurses -- as Veronica Callahan tartly explains to a new doctor on staff -- treat patients, while doctors treat diseases. Recently returned from a military tour in Iraq and with deeper medical experience than most of the facility's residents combined, she -- along with fellow nurses Sonia, a jaded veteran, and naive newbie Chloe -- navigates life both inside the hospital and out. Complicating matters is hospital newcomer Dr. Chris Sands, with whom she shares a past.