The Intelligence Unit's pursuit of a powerful kingpin, the aftermath of a detective being kidnapped and tortured, and a crossover event with Law & Order: SVU.

A tough case involving chasing down Chicago's most wanted leads to the abduction of Halstead. Olinsky calls in a distraught and spiraling Lindsay to help find him. Someone unexpected from Olinsky's past shows up. Roman expresses his concerns to Burgess' about her engagement.