Longtime partners Quinn and Velazquez are chosen to solve the case of Apriel Allen, a woman who was murdered in her apartment two years prior; the detectives begin with a clean slate and hope to bring some peace to Allen's loved ones.

After a homeless man is shot and killed, Quinn and Velazquez assume it's a simple case; after reports come back matching the murder scene to other ongoing murder cases, the detectives realize they're on the trail of a serial killer.