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).

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.

A husband makes a request following his wife's death; Dr. Charles tries to reason with a patient who wants to remove his own arm from his body; a child arrives at the hospital after swallowing magnets; Sarah has last-minute thoughts about her residency.

April and Dr. Halstead clash over how to treat an alcoholic homeless man with a broken leg. Also, Dr. Manning continues to grieve over her husband's death; two elderly women with the same symptoms share a surprise link; Halstead mulls over a job offer in California.

Several patients are discovered to have the same rare infection, prompting Dr. Charles' daughter Robyn, an epidemiologist, to be brought in to find the common link. Dr. Choi and Dr. Rhodes work on an elderly man who is discovered to be very ill, but a conflict in how to best treat him develops between his son and his young girlfriend. Meanwhile, Dr. Reese tries to help a young drug addict and Maggie tends to a patient who is dear to her heart.

Dr. Halstead and Dr. Manning deal with two warring brothers who are brought together when one finds himself in desperate need of a kidney. Dr. Reese's former patient Danny comes to a crossroad. Dr. Rhodes and Dr. Latham treat a 16-year-old girl with a genetic condition in need of surgery, but whose overprotective mother disagrees with that course of action. A convict with unusual intentions puts himself in the hospital and Dr. Charles meddles in his daughter Robyn's personal life, much to her dismay. Meanwhile, Dr. Halstead and April make a discovery that complicates her treatment for TB.

Dr. Rhodes convinces Dr. Latham to join him for a medical trip out of town. Dr. Manning treats an 8 year-old cancer patient who wants to give up on his battle. Elsewhere, an unhealthy woman with heart problems is brought in and doesn't want to listen to doctors. Meanwhile, Dr. Choi, Dr. Charles and Dr. Reese work on a complicated case involving a woman with a personality disorder.

A suicide shakes the staff. Dr. Choi and Dr. Halstead face off over how to treat a patient with stroke symptoms. Family turmoil unfolds when a boy is treated after falling in a river. The importance of learning from mistakes is emphasized to Dr. Reese.

Dr. Rhodes fights to save a mother who's desperate to help her daughter beat cancer. Dr. Charles asks Sarah to conduct his daughter Robin's psych evaluation. When Will and Dr. Manning spend more time together at work, Nina goes to extreme measures to get Will's attention. Meanwhile, Dr. Choi puts pressure on Noah when a residency spot becomes available.

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.

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. 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.

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.

A power outage at Med puts multiple patients at risk and tests the skills of the staff and their enthusiastic med students; Natalie returns following her traumatic brain injury; Ethan and April wonder if a family is in their future.

The team deals with the aftermath of a school bus crash. Dr. Charles worries Dr. Halstead is putting his medical license in jeopardy. Maggie helps a friend in need.

Dr. Charles and April team up to take on a mysterious patient in the ED. Dr. Halstead is forced to make a life-or-death decision for one of his trial patients. Dr. Marcel is confronted by his past when a former acquaintance is brought into the ED.

Crockett deals with a patient who ends up having more in common with him than he thinks. Will and Ethan clash over a pregnant patient with an irregular heartbeat.

Crockett worries he made a surgical error when a recent transplant patient comes in with complications. Carol is once again in distress. Will and Natalie must take action to right their wrong.

Dylan and Charles treat patients suffering from Glass Child Syndrome and misdiagnosed ADHD. Crockett has to navigate hospital politics when he cares for the daughter of a transplant surgeon. Will and Stevie must lay egos aside to help save an elderly patient.

Crockett and Blake clash with Randall when a famous alcoholic football player needs a liver transplant. Dylan is reluctantly reunited with old friends when their son breaks his arm. Stevie and Charles work together when a patient falls ill after back-alley plastic surgery.

Rival gangs bring their war to Med. Halstead and Charles work with a brain cancer patient who's refusing treatment. Tensions run high in the OR when a patient's transplanted uterus fails.

Dylan and Ethan treat a patient shot during a drug raid. Charles and Vanessa work together to properly diagnose a motivational speaker. Will and Hannah must turn to Crockett for help with a patient who's pregnant.