During a routine traffic stop, Gail and Andy find a teenage boy bound and gagged in the trunk of a car; Oliver, Chris and Swarek track a gunman.

When a tenement-building shooting leads to the discovery of an executed gang leader, 15 Division must race to find the killer before a gang war breaks out. As the murderer zeroes in on the one witness who can tie him to the crime, Andy and her rookie, Duncan, are put to a life-and-death test of true police heroism.