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.

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.

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.

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.

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.

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.

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,

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.

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.

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.

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.

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 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.

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.

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.

A new surgical attending Cole Guthrie joins Angels Memorial with the help of his estranged father and clashes with Leanne over their contrasting approaches to medicine. Christa has a crisis of confidence in the middle of a procedure on her first infant since the loss of her son.

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.

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.

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 must handle all emergencies at Angels Memorial that happen outside the emergency room; Malaya arranges a bone marrow drive for Carla; Leanne turns down a date.

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.

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

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.

Leanne visits a prison to finally confront the drunk driver who killed her family. Meanwhile, Malaya begins to feel uncomfortable around her patient.

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.

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.