The murder of a Watershed Management employee uncovers a cold case, and prompts the serial killer at its heart to come out of retirement.

When a normal quinceañera erupts in violence, leaving multiple people dead, the detectives work quickly to follow a lead. During their search for answers, they find a young boy protecting acres of marijuana and discover he is the only witness that can help the case. As the detectives begin to close in on a suspect, Winters receives a surprise visit at home. Meanwhile, DDA Morales (Alfred Molina) must risk upsetting the Mexican government by prosecuting the guilty, which results in a shocking decision.