Dr. Leanne Rorish puts her new first-year residents right to work at Angels Memorial Hospital, Home to the nation's busiest ER.

Christa saves a woman's life and then pleads with Neal to perform a surgery that will save the patient's reproductive future.

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. Mario bullies Angus into performing an unnecessary operation and lets Angus take the blame when Leanne finds out.

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.

Neal clashes with his neurosurgeon father over how to treat his gravely ill mother, whose mysterious symptoms force Angels Memorial to quarantine Trauma One.

Leanne struggles with whether to treat a police officer who helped her during an accident or his shooter, who has more serious injuries. Meanwhile, Malaya's pregnant ex-girlfriend arrives at the hospital with pain in her arm, and Malaya is shocked by her MRI results.

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.

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.

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,

The ER adjusts to the new department head who questions Rorish's decisions. An ambulance arrives with its paramedics knocked out by their patient, who attacks Jesse. Later, Jesse has a heart attack. As the doctors try to save him, other patients include a man hit by a train, the daughter of a controlling Beverly Hills mother, and the wife of a veteran who is struggling with addiction. Meanwhile, Mario leaves the hospital to find the train victim's son with intellectual disabilities, against Hudson's orders.

Leanne, Neal, Christa, Angus, Mario, Malaya, and Heather are sent to the scene of a multi-car collision on a canyon road above Los Angeles. Leanne clashes with the physician in charge, making a decision he questions. Christa treats an injured family whose car is in a ravine. Angus, Heather, and Mario help a man stuck in cement. Mario and Heather find their lives in danger when a patient's husband holds them at gunpoint to save his wife. Meanwhile, Jesse recovers from his heart attack.

A love triangle begins to develop between Mario, Angus and Heather, while the doctors treat patients from a chaotic multi-vehicle accident. When Malaya learns Carla is at the hospital, she goes against Carla's wishes and stays by her side during the delivery of her baby.

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.

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

The doctors are questioned following a violent incident inside the hospital that leaves two doctors gravely injured. Neal and Christa make their relationship to the next level after officially disclosing their romantic relationship to HR.

Christa becomes insecure in her new relationship with Neal when his ex-girlfriend, Dr. Grace Adams, returns to Angels Memorial after spending a year volunteering in Haiti. Also, New York Giants Pro Bowl wide receiver Odell Beckham Jr. comes to the ER to convince his stubborn high school football coach, Pete Delaney, to have life-saving surgery.

Christa and Grace deal with a teenager who claims to have been abused at a camp. Angus begins to take ADHD medication to remain focused. Leanne deals with a VIP patient who had embryos implanted in her without her husband's acknowledgement. Christa feels at odds with Grace.

Mario confronts Angus about his Adderall abuse and Christa is surprised to learn how romantically involved Neal and Grace were before she left for Haiti. Also, Dr. Mark Taylor returns to help Leanne find the money in their budget to keep Jesse and the nurses from walking out.