Jaime goes undercover with a deadly human trafficking ring. Danny and Baez investigate a homicide connected to Darryl Reid, Danny's old partner. Also, Frank grapples with whether to publicly support Mayor Chase on a policy decision and Eddie is determined to teach a young shoplifter a lesson.

Danny and Baez join forces with Danny's old partner, Jackie Curatola, when a serial killer reappears. Also, Eddie faces backlash when she tries to help a woman who accuses a sergeant of rape.

Frank grapples with the personal loss of his best friend and how best to help Tess Ross, the daughter of his best friend, when she lands in jail. Also, Jaime and his nephew, Joe Hill, race against the clock to reunite a trafficking victim with her sister; and Danny and Erin clash when she goes behind Danny's back to use his criminal informant in an investigation.

Danny reunites with a troublesome teenager from a past case when the youth finds herself in danger. Also, Frank faces a difficult personnel decision close to home; Jamie grows suspicious when Henry is asked to be interviewed for an investigative web series; and Erin and Anthony investigate when Erin is the alleged target of a shooting.

Erin is designated to lead a federal investigation into corrupt horse racing. Also, Jamie investigates a drug trafficking operation involving rival gangs and Danny and Baez look into a series of assaults in Little Vietnam with the help of a familiar face.

Danny and Baez investigate a homicide involving voodoo with the help of Baez's old partner. Also, Eddie and a fellow officer team up with Captain McNichols when they suspect a prestigious school is employing discriminatory admission practices.