Assistant State's Attorney Peter Stone prepares to prosecute the accused arsonist in the Kimball warehouse fire that killed 39 people. But his boss, Mark Jefferies, asks him to find a concrete motive for the crime. Stone's second chair Anna Valdez uncovers that the warehouse may have been used for child sex abuse, and believes Dylan could have been a victim out for revenge.

Durther doubt is cast on the case as Stone suspects that Dylan did not actually confess to Detective Olinsky. Antonio admits that he did not actually hear the confession; only Voight and Olinsky did. Voight tries to persuade Stone to let him testify to the confession, but Stone turns him down and agrees to defense's motion to suppress the non-existent confession.

Defense attorney Albert Forrest chooses to represent Dylan. He immediately attacks the credibility of Stone's best witness by getting her to admit that she was under the influence of drugs and alcohol on the night of the fire. Stone does everything he can to fight back, even as it might put his own credibility at risk.

Ultimately the investigative team uncovers that Dylan started the fire to get revenge after one of the victims went to the rave rather than be with him. Stone is further able to cross-examine Dylan on the stand and get under his skin, and the court delivers 39 guilty verdicts getting justice for all involved.

This episode concludes the story that started on Chicago Fire Season 5 Episode 15 and continued on Chicago PD Season 4 Episode 16.