April and Noah are manning the aid station at the Chicago Marathon when a pedestrian is hit by a water cart. Paramedics are unavailable due to rolling blackouts and the marathon. Against April's wishes, Noah inserts an improvised chest tube after watching a youtube video. Sharon sends Will and Nina, who are in the race, to help. When Will arrives, Noah is having trouble intubating the man. As the man's condition worsens, Will is forced to make a difficult call, and opens Ignacio's chest right in the med tent. In order to keep him alive long enough to make it to the hospital, he needs to be put on bypass. The ED has an prototype of a portable machine; Sharon sends Jeff Clarke to Grant Park with it on foot. When the team makes it to the hospital, Connor is less than thrilled with the steps they've taken. Will keeps freaking out because he went against protocol and his history with nonSOP treatments to save patients hasn't been great. When Ignacio is out of surgery, Will waits by his bedside. Conner (incorrectly) performs a neuro assessment that indicates Ignacio will be paralyzed. Later, against Will's warnings, Conner pushes meds to wake the man up. The doctors are concerned at first that he can't seem to push his foot down, but then the realize he can wiggle his toes and will likely make a full recovery.
Nat treats a little girl who is experiencing hearing loss. The mother claims that the girl's father is dead but that she hasn't told her yet because she doesn't know how and Nat asks Dr. Charles to consult. When little Phoebe's CTs come back, they indicate past abuse. When the doctor's confront the mother about the abuse she explains that her ex isn't actually dead, but she suspected him of hitting Phoebe, so she took her and changed their names. The docs are compelled to notify the authorities. Nat notices another symptom in the girl, and right as the cops are taking away the mother, she confirms that Phoebe has a genetic disorder that causes her bones to break very easily. There was never any abuse, just a disease.
Sarah's mother bails on a visit at the last minute, sending a check for $1000 instead. At first Sarah is pissed off, but after seeing what Phoebe's mom went through for her, she seems to experience some forgiveness and understanding for her own mother.
Choi treats an elderly woman for heat exhaustion. Jeff didn't take a full history when she first came in and almost mistreated her, leading to him being bounced from the case. When test results also show that the woman is malnourished, Choi calls in Charles. He recognizes an enzyme level that indicates the woman has taken to eating cat food -- a common thing amongst elderly women who are in financial distress. Choi figures out that she's selling some of her pills to try and make ends meet, but the woman takes offense when he brings it up. When her neighbor and friend arrives, Choi suspects that there's a severe case of "keeping of with the Jonses" going on, and speaks to her instead. It turns out that the neighbor is also facing financial difficulties, and only appears to be doing well because of gifts that her son sends. The two women come to a tearful understanding when the neighbor comes clean with the patient.
Sharon officially files for separation from her husband.