Doctors and nurses fight to save lives in the country's busiest ER. 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.

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.

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. Also, 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 father, Dr. Peter Hudson, who is a neurosurgeon, over how to treat his gravely ill mother, Asra Hudson, 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,.

Leanne becomes rattled at the thought of losing Jesse, as he fights for his life after suffering a massive heart attack. Meanwhile, Mario asks the residents to cover for him so he can search the city for a patient's son, which goes against Neal's direct order not to leave the hospital.

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.

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.

Angus' older brother, an "all-star" ER doctor returns to Angels Memorial in hopes of securing a position as an attending and Christa's romantic feelings towards Neal begins to grow. Also, Malaya has to deal with a patient, Gordon Heshman who becomes obsessed with her

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

The doctors are questioned following a unhappy incident inside the hospital that leaves two doctors gravely injured. Also, 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 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.

Mario comes to the decision to confront Angus. Dr. Mark Taylor attempts to help Leanne find some money in the budget for the nurses.
The team deals with all the injured people from a collapse ceiling during a political debate between Senator Stringer and his opponent. Both families were present and they are all injured.
The personnel confront Leanne and the director of the hospital to get more people working. Jessie gives them an ultimatum but the collapse ceiling put everything on hold.