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.

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.

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.

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.

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.

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. 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