Tensions and tempers are running high when Maggie assigns Nat and Will to work a peds case together. The parents have had the boy diagnosed with something called PANDAS...a diagnosis not accepted by the medical community at large. The treatment involves long term use of antibiotics, which have killed off all the probiotics and healthy flora in the boy's digestive tract, allowing superbugs to flourish. Will bristles about Nat's decision to not challenge the PANDAS diagnosis -- she's willing to go along with the parents as long as it allows them to treat the boys immediate issue. Will finally lashes out at Nat, conflating her decisions about the parents with her decision that they be on a break. Nat picks up on the mother's OCD, and has a conversation with her about it away from the husband. The wife eventually comes clean and they send the boy up for surgery, but the parent's relationship takes a serious hit. Nat apologizes for Will for letting her insecurities get the best of her, but still doesn't forgive him for his indiscretion with Maia. 

Ethan is frustrated by Emily's irresponsible behavior and lack of gratitude to him. But she's the one who is able to convince his patient from the homeless encampment to come in for testing...although she fibs to make it happen. The boy was adopted and never bonded with his adoptive parents due to attachment disorder. Ethan insists on tracking them down because the kid will need a clean, safe space to live while he receives treatment. Ethan locates the parents, but Emily has taken the teen back to the encampment. He's very attached to his dog, and only agrees to return to the hospital if his dog can come with him while he recovers. Ethan finds out that Emily has been homeless in the past, and starts to wonder if his sister may have attachment issues of her own. 

April and Noah treat an elderly man who has inadvertently dosed himself with a large amount of phentanyl. The daughter doesn't show a lot of faith in Noah, causing April to try to intervene as a big sister. Noah calls her own it, but after their patient dies, acknowledges how happy he is to have her because they'll never have to go through what the patient's daughter is going through alone. The discovery of the phentanyl causes the ED to shutdown while it's decontaminated. The board tries to override Sharon's decision to put the ED on bypass, but she goes and reads them the riot act, pointing out that having just one patient go into respiratory failure because of the substance would cost more than the bypass will lose the hospital. Peter warns her that she's on thin ice with the board and that there are grumblings about firing her.

Sarah struggles with the decision to visit her father, who is dying, or not. She finally decides to pay him a visit, and he attacks her, accusing her of stopping by just to make herself feel better and questioning if she too has a personality disorder. Connor, who has just finished reconstructing to transplant for Robert, mentions that his temperature is high and that's a contraindication for the procedure. After a momentary internal struggle, Sarah claims that his temp always runs high, so 99 is normal for him. The transplant looks like it was a success...for now. 

Connor's father sends Ava flowers, which makes Ava jealous. He assumes she's been seeing his father romantically, and she doesn't correct him. When she meets up with him in the cafeteria, it's apparent that their relationship is strictly business...although Cornelius is angling for more. Ava rejects him quite decidedly before walking away, disgusted at his come on. After a surgery together, Connor admits to her that it wasn't the idea of her dating his father that bothered him so much as the idea of her dating anyone. She comes clean about her relationship with Cornelius, and acknowldges that she enjoyed his jealousy.