A shooting outside the hospital injures April and leaves the ED shaken up; Halstead returns after a stint in the witness relocation program; Charles and Elsa have an emotional confrontation; Bekker is reluctant to attend an event honoring Rhodes.
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.
Dr. Halstead rushes to rescue Dr. Manning from a chopper crash. Drama between Dr. Rhodes and Dr. Bekker boils over. Dr. Charles and Dr. Choi work to help a patient with their addiction. April helps Elsa deal with losing her first patient.
Halstead hides the theft of his gun from a suspicious Manning. Tensions are still high between Connor and Bekker, who take a risk operating on an HIV-positive patient. Hank breaks down when he sees a patient from his past.
Connor, who is in hot water with the hospital's Oversight Committee, handles a gunshot victim with unexpected ties to Halstead. Maggie feels guilty about the return of a former patient. Charles has an awkward first date.
Natalie and Maggie witness a pickup truck plow through a street fair and must make tough decisions on the fly. At the hospital, doctors and nurses are on high alert with the influx of patients. Dr. Charles' ex-wife comes to town with news.
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 Dr. Manning disagree on how to handle a patient who they discover is poisoning herself. Dr. Rhodes throws some serious accusations at Dr. Bekker. Dr. Halstead has suspicions about Natalie's new boyfriend. Dr. Choi tends to Bernie.
Caroline shares news that forces Dr. Charles to make a serious decision about their relationship. Maggie meets her sister's new boyfriend but danger may lie ahead. Dr. Rhodes experiences a huge loss. Dr. Choi and April face an unexpected challenge.