After a sex offender is found dead and mutilated, the Intelligence Unit realizes his injuries don't align with his cause of death, leading the team on an unexpected pursuit; Halstead forces Lindsay to confront the truth about her biological father.
A young woman's murder shows apparent links to a series of unsolved killings, but it may be more complicated than it appears; Lindsay agrees to meet her biological father, while Halstead insists on investigating his background.
After Severide is implicated in a hit-and-run and cannot recall the events of the night, Voight and the Intelligence Unit work around the clock to uncover the truth. Meanwhile, Lindsay considers the idea of meeting her father.
The police force is shaken after one of its own is targeted by a cop killer; Voight and team put everything on hold to identify the perpetrator from a long list of suspects and stop his violent rampage.
When a baseball player is the main suspect in a young girl's murder, Voight and team dig for the truth - and Olinsky, who has a history with the athlete, may be their secret weapon. Meanwhile, Lindsay receives flowers from an unknown party.