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.

Devon's doubts about his relationship reach a peak as his friends and family gather for his big wedding day. As Chastain's leading medical device company, Quovadis, continues to succeed, Julian makes a discovery that leaves her uneasy about her involvement in it all. Meanwhile, Conrad continues to work on his relationship with Marshall and Bell takes a risky offer in order to make a mistake from his past disappear.

Lane Hunter's victims and their families become outraged when she is released from prison. Bell, although responsible for posting Lane's bail and getting her released, continues to be tortured by her manipulation. Meanwhile, Conrad uses work to cope with the news about his father, and he teams up with Mina, Kit and the Raptor to treat a patient who is suffering as a result of Lane's dangerous treatments. Then, Devon grows worried when he doesn't hear from Julian, and Nic sets her sights on a primary physician for their new clinic.

When a nasty flu season turns out to be masking a terribly infectious disease, Chastain must race to quarantine and diagnose infected patients. Mina finds herself testing Quovadis medical devices in an effort to defend Dr. Austin, who, feeling responsible for the death of a patient, is serving penance by staying away from the OR. Conrad is prepared to take the next step with Nic, but finds that she may not be as ready.

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.

When Conrad's attempt to surprise Nic with a lavish Valentine's Day dinner is foiled, he gives the reservation away to someone who could really use it. Mina and Devon distract themselves from all Valentine's celebrations by trying to figure out how their seemingly healthy neighbor has suddenly passed away. Meanwhile, Kit gives dating advice to a sex-injured patient, Irving hits a crossroads in his not-so-secret relationship with Nurse Jessica, and Bell decides to celebrate the day in the OR.

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.

When a police officer brings in an injured criminal, the staff must keep him alive. Nic gets roped into a surgical rotation with Cain that leaves her questioning the way he operates. Conrad makes a shocking discovery about the hospital.

After a plane crashes in Atlanta, Devon is overcome by guilt at the thought that he could have prevented it. Adaku returns to ask Mina a big favor. Conrad and Nic consider risking it all to investigate a drug that might be linked to Jessie's death.

On National Nurses' Day, the nurses are severely understaffed and overworked. Cain performs a dangerous surgery on a new patient. Conrad discovers that his father has been administered the same drug that he fears played a role in Jessie's death.

After being terminated, Conrad has difficulty figuring out his next step and distracts himself by accompanying a patient on a zero-gravity adventure. Cain puts the doctors on a commission-based pay system. Bell's company gets its big break.