The doctors work with the Center for Disease Control and Prevention to find an antidote to the deadly viral outbreak at Angels Memorial. Also, Leanne makes a life-changing decision, and Jesse welcomes a new batch of residents.

The ER is quarantined when a viral outbreak jeopardizes the lives of the doctors and patients at Angels Memorial. Also, Ariel, the young girl Leanne bonded with a year ago when she lost her father, returns to Angels.

After pulling a double shift, Mario risks his own life when he follows Willis to a construction site where two brothers are trapped on a crane 300 feet above the ground. Also, Leanne treats the wife of an orthopedist from Angels Memorial who is brought into the ER with mysterious injuries.

As Guthrie takes on a new position as the hospital chaplain, he considers having a risky surgery to treat his Parkinson's. Also, the doctors treat patients who arrive at Angels from an apartment fire.

Leanne defies Campbell's order and uses the hospital helicopter to reunite a family for the last time. Also, Willis and Noa use a cell phone app to communicate with a young girl with autism.

A CODE BLACK at Angels Memorial takes a turn for the worse when a city- wide blackout leaves the hospital without power or back-up generators. As Campbell and Leanne divert high-risk patients to a nearby care center, Elliot and Heather are trapped in an elevator with a woman in labor, and Willis and Dr. Nolan try to help a 92-year-old woman who thinks it's 1942,

A 13-year-old girl who arrives at Angels Memorial following a seizure turns out to be Campbell's daughter; the team treats a deaf woman and her translator after they survive an automobile accident.

Willis, Leanne and Jesse put their lives on the line to operate on an officer with an explosive bullet in her leg; Mario, Noa and Guthrie tend to a magician with breathing trouble.

The doctors treat cult members who unwillingly survived a mass suicide attempt, and Mario decides to connect with his late father's girlfriend.

Willis and Campbell are sent to a Russian submarine in U.S. waters to treat a sailor badly wounded during an explosion, and violent convicts injured during a prison riot descend upon Angels Memorial.

Malaya must inform a college student who regains consciousness at Angels Memorial that she's the victim of a rape, and Willis and Campbell butt heads over a terminally ill woman who wants to end her life on her own terms.

The Angels Memorial doctors treat victims caught in a landslide, and a group of children come in from a camping trip with measles putting the entire ER at risk.

On Halloween night, Willis, Noa and Elliott rush to the scene of a fire at a haunted theater, where Dr. Nolan and her boyfriend's son are trapped.

Willis, Mario and Heather perform a radical operation on a maintenance worker stuck under a boiler that exploded; Angus' father tries to seize power of attorney over Mike, who remains in a coma.

Willis must help a promising young soccer player make a life-altering decision after he's seriously injured when a bus carrying his entire team crashes, and another patient's hesitation to share that she's transgender makes it difficult for the doctors to diagnose her severe abdominal pain.

Colonel Ethan Willis joins the team as part of a program in which the Department of Defense sends doctors to hospitals to teach new techniques.