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 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.

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.