The second part of the One Chicago crossover kicks off with Intelligence responding to the scene of the fire. 

Roman was there because he was trying to confront Logan Peters, the 25-year-old dealer reportedly dating his sister, Sarah, who was missing. 

Burgess and Voight ask why Roman didn't involve them in his search for his sister, and he admits it's because Sarah was an addict who was helping Peters sell his tainted drugs. 

He's worried that if she sold the drugs that killed several of her classmates, she would be arrested and her life would be ruined. 

Despite Roman not being a cop anymore, Voight allows him to ride with Kim under a "short leash."

Roman asks Burgess why her unit seems to be walking on eggshells around her, but she changes the subject.

After questioning some of Sarah's "friends," they check out a cabin where she was last seen partying. 

Burgess finally tells Roman about her loss, and he's sympathetic. 

They find Sarah's coat outside and then see her frozen body laying by the river. 

Fire is called to come saw her out.

An autopsy determined that Sarah was beaten, strangled, raped, and then left to die in the cold for about 19 hours. 

Roman feels the guilt creep in. He arrives at his home to tell his parents. 

When he does, Roman's father punches him in the face and accuses him of not being there for Sarah when she needed him. 

The next day, Intelligence gets wind of a possible warehouse where Logan Peters might be hiding out at. 

Upon arrival, they hear gunshots and rush in where they find a man overdosing. 

A witness comes forth placing another gang member's car at the scene, but the evidence doesn't add up. 

When Burgess cross-examines the witness, she realizes that he's lying because his story doesn't make sense either. 

She has Platt run the man's record and learns he was Roman's informant. 

She also recognizes the "car" spotted at the scene, the real one, as belonging to Roman's cousin. 

She confronts him with the evidence the night before the funeral, but Roman denies everything. 

The next day at the funeral, most of Intelligence shows up to support him including Voight, who seemingly figured out Burgess was lying to him and that Roman was the man responsible for killing Logan. 

During the eulogy, Roman blames himself for not being there and it's clear he's riddled with guilt, a guilt he promises to carry for the rest of his days. 

Following the service, he is ready to get arrested, but Voight tells him they found no evidence. And since Logan is a scumbag, they aren't going to put too many resources into finding who killed him. 

Basically, Voight looked the other way. 

Both Burgess and Roman are shocked. 

Burgess takes to heart what Roman said about carrying the guilt. 

Earlier in the episode, Burgess and Ruzek have a chat in which Burgess emotionally reveals she's angry with herself for losing the baby. She informs Ruzek she wants him to be angry too instead of understanding and supportive.