Angels Memorial Hospital has the most overcrowded ER in the US. But despite the workload, its doctors work with little resources and a shortage of trained personnel, leaving them to perform near-miracles as they deal with constant influxes that go over their capacity, referred to as Code Black.
Angels Memorial gains another doctor in the form of Col. Ethan Willis, who keeps pushing the rules and butting heads with Dr. Campbell. Mike gets in a terrible situation that will bring consequences for not only him but also Angus and the hospital at large.
Among the many stories happening this season: A girl gets caught up in a shooting during a drug bust, and what the doctors do and how far would they go to save her life. Willis shifts to field medicine, and Lain encounters some tragically familiar situations.