When things become complicated, Will is forced to lie to Natalie. Ethan and April find out some compromising information about Emily's boyfriend and Ava is unsure of what to do with a patient who is refusing treatment.

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 treats a woman on the verge of freezing to death. Dr. Charles' ex-wife receives some concerning news. Choi handles a lymphoma patient with viral meningitis and a complicated family. Manning makes a house call.

Dr. Rhodes receives an alarming phone call that prompts him to rush out in the middle of an important surgery. Dr. Halstead comes to the aid of an FBI agent who is brought into the ER, but he suspects there is more to the story than he is being told. Dr. Manning and Dr. Choi find themselves on opposite sides of a major disagreement over doctor-patient confidentiality.

The hospital goes into lockdown mode when a man with a gun holds medical staff hostage. Goodwin is forced to make a tough decision. Dr. Rhodes begins to realize his time with his father is getting short.

Dr. Charles and Caroline set some major plans. Ava fights to keep her relationship with Connor. Agent Lee informs Will of news that may put his life in danger.