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.

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.

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.

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.

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.

When the lead actor of the musical “The Lion King” tour arrives at Angels Memorial with a throat infection, Leanne gives him a diagnosis that puts both his career and life in jeopardy. Also, the doctors and the cast of “The Lion King” help a 17-year-old boy deal with the difficult decision of taking his father off life support,

After a violent incident inside the hospital results with some grave injuries, the doctors are questioned. Christa and Neal admit their relationship to human resources.

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 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, 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.

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.

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.

Heavy fog at the scene of a massive multi-vehicle accident puts the doctors in danger; Jesse's confidence has taken a hit; Carla's condition turns critical.

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.

Four new first-year residents are immediately put to work by the ER's tough-minded residency director Dr. Leanne Rorish.

Christa saves a woman's life and then pleads with Neal to perform a surgery that will save the patient's reproductive future. Meanwhile, Mario gets into a fight with a patient after he delivers a diagnosis that could end the man's hockey career.

The doctors work 36 consecutive hours in code black and must deal with a distraught mother of two sons who were in a devastating car accident. Meanwhile, Mario bullies Angus into performing an unnecessary operation and lets Angus take the blame when Leanne finds out.

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.

Angus utilizes his background in psychology when a woman cannot remember how she injured herself and others; Christa bonds with the mother of a patient with cystic fibrosis.

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.

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.

Leanne must deal with the difficult decision of whether to save Tom Moreno (Michael Trucco), the police officer who helped her during her family's accident, or his shooter, who has more serious injuries. Also, when Malaya's pregnant ex-girlfriend, Carla Niven (Shiri Appleby), arrives at the hospital with pain in her arm, Malaya is shocked by her MRI results.

Angus' older brother, an "all-star" ER doctor, tries to secure a position at Angels Memorial. Meanwhile, Christa's romantic feelings towards Neal begin to grow; and Malaya deals with a patient who is obsessed with her.

Christa is feeling insecure after Neal's former girlfriend makes a return to the hospital after a year of volunteering in Haiti.

As the doctors treat patients from the chaotic multi-vehicle accident, a love triangle begins to build between Mario, Angus and Heather. Also, when Malaya learns that Carla is at the hospital, she goes against Carla's wishes and stays by her side during the delivery of her baby. Shiri Appleby guest stars.

Christa has to try and ignore her personal feelings as she and Grace attempt to help a patient who says he was abused at a camp for troubled teenagers.

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.