A member of the Halstead family died during the One Chicago crossover event, leaving characters from all three series in shock.
As the firefighters fought a serious situation in the 20th floor of a residential building, Chief Boden (Eamonn Walker) was interrupted by a worried Jay Halstead (Jesse Lee Soffer), who tells him his dad, Pat (Louis Herthum) lives in the 23rd floor and has not been answering his phone.
After Casey fails to find him in his apartment at first, they realize that he must have gone up to the 25th floor to help a friend, who is in a wheelchair, to safety. Though when Casey finds them at his friend's apartment they are both unconscious from smoke inhalation.
Despite a stressful struggle, the firefighters are able to send the two men down, and Jay heads with his father to Med to treat his inhalation injuries — remembering that he also had a serious heart surgery less than a month before the fire.
At the hospital, Pat lashes out at Jay — blaming him for being in the building because he forced him to sell his house. When Will (Nick Gehlfuss) refuses to stand up to his father and defend Jay, he gets angry and walks out.
"All those times you said you couldn't leave the hospital, who took care of Dad? Me," Jay says to his brother outside of Pat's room, bringing up old wounds about their family's relationship.
"I do plenty for dad, I still do. Who goes and checks on him? Who makes sure he takes his meds?" Will responds.
"I'll tell you what, when he gets out of here, find him his next apartment," Jay says before he walks out.
The situation becomes more dire when Pat's heart stops, and with all other doctors busy, Will has to perform the code blue on his own father, as Jay watches. Later, Will reveals it took him five minutes to bring his dad's heart back, but since he has no brain activity he is pronounced brain dead by the neurologist.
Jay and Will are both heartbroken by the development, but Jay doesn't understand that there is no hope that his father will ever wake up. The brothers have a disagreement about whether or not to unplug him, which leads to Jay punching Will in the face.
As he mourns his father in the terrace, Natalie (Torrey DeVitto) finds him and comforts him about his father's death.
"Your dad knew you loved him, and so does Jay," she says after Will expresses his regrets for not being there more for his family.
Later, Will returns to his dad's room and apologizes to Jay for not being there for them and not giving him time to grieve. Jay, left brokenhearted by his father's death, admits he knows Pat is gone, and the brothers sit together and quietly say a final goodbye before the pull the plug.