Devon and Conrad race against the clock to save the life of a woman who is deteriorating fast from undetermined symptoms. When the patient turns out to be a hero who helps previous criminals get their lives back together, the team relies on her family of ex-cons to help diagnose and treat her. Tensions rise as Nic continues her search for evidence to incriminate Lane, but must simultaneously tend to her sister, Jessie, who is rushed into the ER. Meanwhile, York returns to the hospital with his mother, who is in need of a risky procedure, and comes face-to-face with the stone-cold Dr. AJ Austin.

Halloween at Chastain proves to be just as spooky as ever when Conrad is tasked with diagnosing a young woman admitted to the hospital with extreme night terrors. Meanwhile, Devon faces his first Halloween in the ER, Nic panics over her decision to bring her newly sober sister to Mina's epic annual Halloween party and Bell finds an interesting way to make use of his new assistant.

When patients from the hospital's prescription drug trial start suffering life threatening side effects, Nic fears that her sister Jessie may be in danger. As a result, she and Conrad work to convince Bell that these trials are not worth the risk. Meanwhile, Mina, Austin and Kit must set aside their competitive nature and work together on a patient whose health is quickly deteriorating and Devon uses Julian as the beta tester for a product he's designed.

Conrad, Kit, Mina and the Raptor work to save the life of a med student in need of a triple-organ transplant, drawing Bell back to the OR for one of the Chastain's riskiest surgeries yet. After the police find Julian's empty car in a nearby lake, Devon does some investigating of his own to find out what might have happened. Meanwhile, Mina and the Raptor hound Bell to halt his business with the risky medical device company, Quovadis, and Nic makes a rash decision regarding her sister.

Chastain picks up the pieces after the fall out with the corrupt medical device company Quovadis, leaving Marshall ready to charter new territory in the medical field, and Devon to finally discover the truth about what happened to Julian Booth. As Conrad and Alec team up to help a young gymnast experiencing mysterious symptoms, Nic focuses on her sister, who's back with their estranged father, Kyle, in tow. Meanwhile, Bell rushes to Kit's aid when her ex-husband comes to the ER needing emergency surgery.

When Atlanta is struck by a severe snowstorm, Mina must perform a big surgery - without the help of The Raptor - to save the life of a young father, while Kit and Bell get stuck babysitting the man's children. Nic and Conrad experience a disagreement with a patient's treatment, causing further strain in their relationship. Meanwhile, Devon teaches an important lesson about life and death to a first-year med student.

Devon grows concerned when a mother's complaints go unaddressed after her delivery, and pushes Bell to take drastic measures. Conrad is faced with breaking the news to Nic regarding Jessie's worsening condition. Meanwhile, The Raptor, Mina and Kit spring into action when a mother and son enter the ER with devastating injuries.

When the hospital has a severe blood shortage, Conrad must try every avenue to save a patient's life. Nic receives devastating news and is left worrying about her sister's health, while Mina and Devon work with a new anesthesiologist who is not what she seems. Elsewhere, Kit considers the future of her intertwining relationships and Bell has an encounter with a woman from his past.

Bell hopes that a lottery winner who was admitted to hospital could serve as a way to solve Chastain's financial struggles; Nic is irate with Alec for suggesting she meet an organ broker; Devon and Irving help Mina remember certain details.

In an effort to save Chastain, Bell considers selling the hospital to a conglomerate, but Kit tries to make him see that the negatives will outweigh the positives. With Conrad's help, Nic tracks down Kyle and pleads for him to reconsider donating a kidney to Jessie. Meanwhile, Mina voices her concern to Austin when Shira is assigned to Micah's surgery and Devon fights for the care of a patient whom the doctors suspect is uninsured.

The doctors of Chastain are surrounded by new rules and doctors, as Red Rock Mountain Medical takes over the hospital. Conrad finds himself in a dangerous situation when the construction for a new neurosurgery center causes a gas explosion.