A member of Firehouse 51 clings to life and takes a sudden turn for the worse as medical staffers race to give treatment. Meanwhile, Dr. Natalie Manning prepares for her pregnancy and members of Chicago P.D. probe the case of a woman pulled from a fire.

The crossover starts on Chicago Fire S04E10 The Beating Heart (I). It continues on Chicago P.D. S03E10 Now I'm God (III).

Dark family secrets emerge when Dr. Rhodes' father is honored for making a large donation to the hospital. Meanwhile, the Department of Homeland Security arrives when two injured airplane stowaways are brought to the hospital and Dr. Sarah Reese must deliver heartbreaking news to a boy.

Dr. Rhodes and Dr. Choi clash over the final decision made by a dying patient. Meanwhile, a pending lawsuit against Dr. Halstead moves forward, and doctors race to save a patient with a misdiagnosed flesh-eating bacterial disease.

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.