A warrior named Akecheta explains his life story to a child, beginning with the early days of the park. He dedicates himself to finding the truth and searching for a door to another world.
The staff of the ER unit of Chicago's County General Hospital return for the final series. Neela proves her worth as attending material when she clashes with Dubenko on how to proceed with two different surgical cases, while Brenner gains a deep insight into his painful childhood.
Staff in the ER try to come to terms with the loss of their colleague. Meanwhile, the staff bristle at the new Chief's tough disposition. Gates and the new interns treat a bio terrorist, who has a lethal secret that endangers them all, and Neela makes a great effort to get Dubenko back on the surgery staff, and also gets help from an unexpected source.
Chaz, now a med student, begins his ER rotation. Morris takes him under his wing and shows him some risky procedures, endangering a patient and raising Banfield's ire.
With oil company rep Walker Browning (guest star Callum Keith Rennie) on the war path to find Gab and have Henry arrested, and Monte out for blood after the violent encounter with new deputy Zachary, Walt finds himself under pressure from all sides in the season finale. Meanwhile, Nighthorse resurfaces with offers to both Cady and Henry – that is if a suspicious Mathias doesn't find Henry first.