A boy is suffering with a serious fever and his high-strung mother begins to show signs of distress.

Drew and Paul head to the scene of a multi-car collision while the newly-anointed Dr. Ragosa along with Jordan, Scott, Krista and Kenny, manage the deluge of incoming victims. Meanwhile, TC and Topher head into a war zone to treat an old friend.

T.C. and Topher return to find Jordan in critical condition and San Antonio terrorized by snipers; Drew and Gwen get caught in the crossfire when a SWAT team corners the snipers.

Drew takes action when a gunman attacks at a friend's promotion ceremony.

A building collapses during a rodeo; a severely injured cowboy exhibits strange symptoms; Scott causes a serious car accident.

A downtown gas explosion sends dozens of casualties to San Antonio Memorial Hospital.

A horrific crash sends dozens of soldiers, including Drew's boyfriend, to the emergency room, where TC and Scott clash. Meanwhile, Topher tries to diagnose a soldier's illness, and Kenny tries to improve Ragosa's online-dating profile.

TC and Topher treat the lone survivor of a plane crash while fending off an intimidating law-enforcement officer with a secret motive. Meanwhile, Paul is smitten by an injured exotic dancer whose condition takes a turn for the worse; and Krista cares for a teen with an eating disorder.

A shoot-out in the ER leaves Topher seriously wounded. TC tries to control his Afghanistan flashbacks. An explosion at a fertilizer factory sends burn victims to the ER, overwhelming the shorthanded staff. And Jordan discovers a secret about TC.

A violent storm pummels San Antonio, sending numerous patients to the emergency room. Elsewhere, TC and Dr. Scott Clemmens rush to a mudslide disaster to treat a mother and her son; and Topher braves the storm to help his stranded wife, who's going into labor with twins.

An injured skydiver is rescued, but there's more to the case than meets the eye. Meanwhile, the night-shift staffers treat an electrocuted janitor, then scramble to save his wife and children when they fall ill to life-threatening symptoms; and Paul learns about his limitations as a doctor.

TC and Scott fight to save a boy and his mother who were injured in a car accident, yet it becomes clear there's more to the family dynamic than meets the eye. Deployed in Afghanistan, Drew and Syd face the aftermath of an OR shooting.

T.C. discovers his sister-in-law's complicated history after he treats her for a fall down stairs.

As the city erupts in violence over an impending jury verdict, the night shift becomes ground zero when they have to take in the man suspected of the racially-motivated shooting at the source of the unrest. His presence in the emergency room sparks sharp conversation and disagreements among the staff over the highly-charged topic and even close friends Kenny and Paul find themselves at odds. Topher does his best to control the mounting chaos in the ER while out in the field, TC makes a decision as to which of two patients to bring in, leaving Paul and Scott to question TC's motives.

A patient arrives with radiation poisoning, spinning the night shift into chaos and putting it into lockdown. Meanwhile, staffers speed to a serious car crash, where they discover an injured police officer, TC's troubled sister-in-law visits, and a former patient harasses Jordan.

A college co-ed falls from a balcony and once she is in the ER, TC and Paul find that her situation is even more complex. Jordan bonds with a terminal patient who teaches her some important lessons about living. TC's errant sister-in-law Annie returns and hopes to make amends. Meanwhile, Jessica - a pharmaceutical rep with cutting-edge equipment that Scott is so close to getting for the hospital - if her tension with TC doesn't kill the deal.

A fireworks explosion creates chaos at a concert, sending patients streaming into the hospital as TC and Topher race to the scene. Syd returns from Afghanistan and faces her unique family dynamic. Jordan and Scott address simmering differences.

After performing a daring on-site rescue to save a teenage girl, Drew is forced to re-evaluate his priorities as a new father. Back at the hospital, the ER is flooded with mass casualty victims from an amusement park disaster. Hoping to get Paul back on staff, Jordan facilitates a rapprochement between Paul and his father. Meanwhile, Scott pursues a more active role in the hospital and Kenny tries to put Cain in his place.

Topher takes over as chief of the night shift. TC is temporarily suspended. Jordan is scrutinized for her mishandling of the man who shot a recovered Topher. A father is trapped under an elevator. Ragosa returns to the ER.

The doctors race to save Topher's mom when she comes to the ER with life-threatening symptoms. The team discovers a gravely injured foster mom is harboring a secret. Jordan asks T.C.'s girlfriend for help with a patient.

The night shift is tested when a rancher accidentally shoots his wife. TC heads to a teen party to save the life of a young football star. Jordan and Kenny treat a beauty queen in severe distress. Topher makes a decision about his job.

The overnight crew becomes immersed in a bizarre car-accident rescue. Drew serves overseas in Afghanistan and teams with a colleague to treat an Afghani woman, A spunky grad joins the shift.

Drew stressfully adjusts after returning from deployment in Afghanistan. A bride and her wedding party are treated for injuries sustained during the festivities, and Topher's demanding mother pays a visit.

When a bomb explodes outside the hospital, TC, Topher and Drew are forced to make the tough decision to stay and treat the injured or evacuate and begin transfers to nearby hospitals. Everything changes when TC suddenly realizes he may know the person responsible for the explosion. While the team works feverishly to tend to the wounded, the nurses go on strike just when the hospital needs them the most. Meanwhile, throughout the intense night shift, Shannon and Paul attempt to confront each other about something personal.

TC initiates a bar brawl, landing him and Drew in jail for the night. While behind bars, Drew and TC's relationship reaches a breaking point. Jordan rushes her date to the ER, where she's shocked to learn he's not who she thought he was. Topher fights for a patient who many doctors have dismissed. Scott and Annie struggle to save their relationship while Jessica works to win back TC's trust. Meanwhile, Syd meets Brianna, and Rick visits the hospital.