Dr. Rhodes begins a fellowship in cardiothoracic surgery, only to have problems with his new boss, in the Season 2 opener. Also: Dr. Choi is the new chief resident; Sarah receives an opportunity; and April faces her recently discovered illness.

Two complex cases involving sick babies may have a surprising connection. Meanwhile, an upbeat homeless man is treated and offers valuable insight to the doctors; Dr. Choi mentors a military man; and Dr. Reese tries to adapt to her new position.

A mystery illness is investigated when an Indonesian man arrives at the hospital in bad condition. Meanwhile, deep family secrets surface when Maggie takes Dr. Halstead to her family reunion; Dr. Rhodes tackles complex heart surgery; and a woman has an unusual pregnancy.

A same rare infection plagues several patients, resulting in a medical investigation by Dr. Charles' epidemiologist daughter. Meanwhile, an ill elderly man is treated, but a conflict rages over how to best help him, and Dr. Reese cares for a drug addict.

A car accident at the Chicago Marathon tests Halstead, April and her medical-resident brother, who are on the scene and must spring into action. Meanwhile, complications ensue when a girl experiences sudden hearing loss; Choi treats a malnourished woman; and Goodwin tries to get her personal life in order.

Dr. Reese gets a return visit from a troubled teen in a seemingly hopeless situation. Meanwhile, Dr. Manning cares for a young cancer patient but struggles to tell the parents of her dire condition; a logjam plagues the hospital; and Dr. Choi is impressed by a science geek and her friends.

Goodwin reconnects with her childhood sweetheart, who arrives at the hospital in dire straits. Meanwhile, Dr. Halstead gets lured into a business endeavor; a young woman with a heart infection is treated; and Reese's former patient seeks her help.

Two warring brothers are brought together when one desperately needs a kidney. Meanwhile, a teen with a genetic condition is treated, but her overprotective mother resists the course of action, and Dr. Charles meddles in his daughter's personal life.

Two MMA fighters arrive at Chicago Med in poor shape. Meanwhile, Dr. Charles must evaluate a patient as a possible heart recipient; Jeff makes a confession; Dr. Stohl returns from his sabbatical leave; and April faces a setback.

Maggie must face her past when her arresting officer arrives at the hospital with a serious injury. Also, a heart transplant patient gets into a car crash, complicating her surgery; Dr. Halstead treats an uncooperative horse jockey; Manning and Halstead deal with a patient's death.