Goodwin finds herself quickly clashing with the new hospital COO Gwen Garrett while April questions whether or not Ethan's sister, Emily, is using again. Dr. Charles deals with his past actions.

The doctors and nurses of Chicago Med find themselves on high alert when an overflow of patients are rushed into the doors following a terrifying apartment complex blaze. Dr. Rhodes fights to save the life of one of "Chicago Fire's" own, while Dr. Halstead and his brother Jay struggle with their own personal battle.

When a sick boy is brought in, Ethan is faced with a tough decision that quickly escalates into a complicated and dangerous situation. Connor and Maggie are put to the test, while Natalie and Ethan aren't sure what to make of Elsa, the new third year medical student.

Dr. Halstead gets an unplanned visit from the CPD while Ethan is skeptical of a woman who is experiencing chronic pain. Natalie tends to a cancer patient whose brother has strong feelings on why he is refusing to lend his assistance.

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.

Dr. Manning and Dr. Halstead become skeptical of a patient's injuries when the victim of a car accident is brought into the hospital. Ethan and April have a difficult time understanding Emily's attachment to her boyfriend despite recent developments. Will and Natalie brace for their joint bachelor/bachelorette party.

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.

Will adjusts to hospital life in the aftermath of his recent undercover activities. Ethan and April's personal relationship starts to interfere with their working situation. Dr. Charles and Dr. Manning collaborate on a patient suffering from Alzheimer's. Dr. Rhodes and Dr. Bekker have a difference of opinion in dealing with a woman in desperate need of a kidney transplant.

Dr. Halstead rushes to rescue Dr. Manning after she is involved in a Medevac helicopter crash. The personal drama between Dr. Rhodes and Dr. Bekker boils over. Dr. Charles and Dr. Choi work to help a patient come to terms with their addiction. April helps Elsa deal with the loss of her first patient.

Halstead hides the theft of hisballoon 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 aballoonshot victim that has unexpected ties to Halstead. Maggie feels guilty about the return of a former patient. Charles has an awkward first date.

After witnessing a pick-up truck plow through a street fair, Natalie and Maggie are forced to make some tough decisions on the fly. The doctors and nurses of Chicago Med find themselves on high alert with the influx of patients arriving in need of aid. Dr. Charles ex-wife comes to town with news.

Natalie and Will grow further apart. Daniel struggles to come to terms with his feelings toward his ex-wife. The personal issues between Connor and Ava continue to cause problems at the hospital.

When a car unexpectedly smashes through the ambulance bay doors, Dr. Choi makes some difficult decisions in an effort to save a worker trapped beneath the wreckage and April, who's also in danger. Dr. Rhodes and Dr. Bekker tend to a patient whose best chance at survival is an extremely risky heart surgery. Dr. Charles struggles to come to terms with ex-wife Caroline's treatment.

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 aballoon 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.

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.