Voight and the team help Assistant State's Attorney Nina Chapman pursue a drug runner who dodged prison years ago after Chapman's informant mysteriously disappeared. The investigation takes a turn when Voight uncovers a damaging secret from Chapman's past, threatening the investigation and Chapman's career.

When a family is poisoned in their home, the team discovers a connection to the Becks. Ruzek goes undercover to work for their business and as he gets closer to Samantha, chilling information about her father, Richard, comes to light.