Dr. Rhodes second guesses removing himself from the team working to separate conjoined twins; Dr. Choi and April make a startling discovery about his sister; Dr. Charles uncovers troubling information concerning Dr. Reese's father.

Bekker takes drastic action to keep Rhodes from leaving Med for good. Meanwhile, Halstead questions Manning's feelings about their upcoming wedding, Ethan receives shocking news about his sister, and Dr. Charles mourns a loss.

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.

The crossover starts on Chicago Fire S07E02 Going to War (I). It continues on Chicago P.D. S06E02 Endings (III).

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

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.

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.

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.

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 and Dr. Choi tends to Bernie.

Dr. Manning's actions with a recent patient lead to serious repercussions. April and Noah disagree over a patient who is injured after a beating. Dr. Charles is visited by a childhood friend with a surprising revelation.

After a major accident at O'Hare, the E.D. is concerned one of their own is in mortal danger. Will's proposal for a safe injection site goes to the board for consideration. Natalie and Goodwin become concerned for Gwen.

Ethan teams up with an unexpected person to treat a famous tennis player who is afraid his career might be over. Goodwin's new protocols cause a stir.