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.

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.

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.

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,

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.

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.

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.

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.

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.

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.

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. 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.