Dr. Manning returns from maternity leave and treats a teen with a history of medical issues. Meanwhile, Dr. Choi cares for a former Navy shipmate; a Saudi prince arrives for a surgical procedure, but only from a hotshot surgeon; and a romance blooms between Sarah and a lab tech.

A 9/11 hero is treated, but an unforeseen medical problem arises. Meanwhile, Sarah contemplates which hospital to select for her residency; Dr. Choi cares for an injured teen hockey player with a demanding father; and Halstead and Manning clash.

An erratic patient arrives, claiming that his heart is pounding inside his head as he takes drastic measures to stop it. Also, Dr. Manning helps a boy with a broken wrist, but she suspects deeper issues exist; Dr. Rhodes impresses with his skills; and Will receives news about a lawsuit.

April and Dr. Halstead clash over how to treat an alcoholic homeless man with a broken leg. Also, Dr. Manning continues to grieve over her husband's death; two elderly women with the same symptoms share a surprise link; Halstead mulls over a job offer in California.

The hospital is forced to evacuate when a toxic chemical is brought into the E.D., leaving patients and the staff in grave danger. Stuck in an elevator, Dr. Charles and Dr. Manning are forced to take drastic measures with a pregnant woman. Goodwin is tasked with making difficult choices and Dr. Rhodes discovers a secret that Dr. Bekker has been holding from him.

Dr. Charles struggles to convince Dr. Choi that surgery isn't always the answer. Dr. Rhodes finds himself in hot water with Goodwin when he disobeys her direct order. April becomes frustrated with Maggie when she continues to question her leadership role as the stand-in charge nurse. Dr. Manning suspects Dr. Halstead is keeping something from her.

Will and Natalie prepare for their big day, but an unsuspecting Will soon finds himself sidetracked. Dr. Charles disagrees with Goodwin on how to best handle a patient's treatment while Dr. Choi and April are on their own when a pregnant woman delivers. Dr. Rhodes finds himself operating on a patient that is of great importance to Det. Halstead.

April finds herself in a dangerous situation and Natalie gets an update on Will. Dr. Rhodes gears up for a gala honoring his hybrid O.R. and tries to convince Dr. Bekker to join him.

Halstead takes heat for making an unauthorized move to treat his pregnant patient. Choi becomes personally invested when treating a homeless veteran. Rhodes and Bekker deal with a patient who desperately needs a liver transplant.