The new residents are introduced to the ER. A new doctor from the army who knows many advanced procedures is flown to a shark attack on the beach with Mike Leighton and Leighton falls 20 feet from the helicopter. Dr. Guthrie Jr. is promoted to the director of the ER in addition to the OR.

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

Willis defies Campbell’s orders when he helps Mario and Heather perform a radical procedure on a maintenance worker stuck under a boiler that exploded. Also, Angus’ father, Dr. Desmond Leighton, tries to seize Power of Attorney over Mike, who is still in a coma, even though Mike granted that right to his brother, Angus.

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,

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.

Malaya must inform a college student who regains consciousness at Angels Memorial that she's the victim of a rape. Meanwhile, Willis and Campbell butt heads over a terminally ill woman who wants to end her life on her own terms; and a comedian is treated after he collapses on stage during a performance.

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.

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

Willis, Leanne and Jesse risk their lives to operate on an injured officer who has an explosive bullet lodged in her leg. Meanwhile, Mario, Noah and Guthrie treat a magician who comes to the hospital with breathing difficulties.

A 13-year-old girl arrives at Angels Memorial following a seizure caused by spina bifida and the doctors are shocked to learn she is Campbell's daughter. Meanwhile, a workaholic deaf patient and her translator are treated after their car rolls into the Los Angeles River.

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.

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

Guthrie becomes the hospital's new chaplain and considers undergoing a risky surgery to treat his Parkinson's. Meanwhile, the doctors treat patients involved in an apartment fire.

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.

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.

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 doctors must race to save a girl caught in the crossfire of a shoot-out; Willis shifts his focus to field medicine, choosing to work primarily on an ambulance with his new partner, paramedic Rox; Leanne begins her journey to adopt Ariel.

Angus and Mario treat a patient who is a self-proclaimed psychic and envisions the staff singing and dancing, seeing beauty amid the chaos at Angels Memorial. Also, Willis and Rox put their lives in danger to rescue a congressman and his staffer from a multi-car accident.

Jesse is in denial when his brother arrives at Angels Memorial in bad shape after being pinned down in a warehouse collapse and further tests reveal he has advanced congestive heart failure. Also, Willis opens up to Rox about his brother who was killed in Afghanistan.

Willis and Rox arrive at a road rage accident resulting in multiple serious injuries. Also, Elliot doubts his ability as a doctor when he’s sued for his role in the death of the SWAT officer involved in the drug bust-turned-shootout, and Leanne discovers Ariel on an ice cream “date” with Max, a young patient at the hospital.

Over the radio, Leanne and Jesse talk a young girl through how to use the supplies on board a small plane to build a makeshift defibrillator when her mom, the pilot, loses consciousness mid-flight. Also, Rox and Willis are taken hostage at gunpoint while on their way to meet the plane at the landing site.

Willis and Rox are called to the scene of a wildfire in the mountains of Los Angeles to tend to the injured firefighters, and they choose to stay to look for a missing young boy who was separated from his father in the chaos.

Rox decides to make amends with her former step coach when she arrives to Angels Memorial with the local high school step team after a pyramid stunt goes wrong. Also, Noa pleads with Leanne and Campbell to try any other method before performing an emergency hysterectomy on a young teenage girl, who is experiencing complications after giving birth.

Mario joins Rox and Willis on the scene of a boat crash and, in Center Stage, Leanne works to save a brother and sister who drank boiling water through a straw as part of a challenge. Also, Max's father tells Leanne to keep Ariel away from his son after he finds them kissing.

Max is brought to Angels Memorial with breathing difficulty, and Ariel tells him she loves him. Also, Rox accompanies Willis and Martin to the funeral of an army buddy of Willis' brother, and Willis decides to get to the bottom of what happened to his brother's unit.

Elliot fears the worst after hearing the emotional testimony by Detective Gomez's wife at his malpractice trial, but he hopes footage Diego shot for his documentary will change her mind. Also, Rox attempts to connect with Willis but he pushes her away, and Leanne attempts to comfort Ariel in the wake of a devastating loss.

While rescuing an injured firefighter, Rox is hit by a drunk driver and rushed to Angels Memorial. Willis begins to realize his feelings for Rox and goes to great lengths to help her. Also, Leanne is excited to tell Ariel good news about her adoption.

Willis continues to tend to Rox's medical needs in San Diego and Leanne and Max's father go searching for Ariel. Also, when Noa reveals to Mario she wants to take a job offer in Philadelphia, and Campbell offers Mario the attending position at Angels, they realize their career choices will mean ending their relationship.

Angels Memorial descends into chaos when a plane crashes into the 8th floor. Also, Noa has a car accident and it is up to Mario to save her life. Also, Willis admits to Rox that he needs her in his life and the doctors gather in court to support Leanne for her custody hearing.