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.

After immigrant Mamadou Berry is murdered, Quinn and Velazquez seek to find his killer; the yearlong investigation pits the detectives against the International Robbin Crew, a ruthless and deadly Atlanta gang.

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.

When Detectives Quinn and Vince investigate the shooting of Antwan Curry, they find a trail of blood leading away from the murder scene; they set out to find the injured person, not knowing if they're looking for another victim or the killer.

Cassandra Bryant, 38, is found naked and barely clinging to life; she dies in the ambulance before identifying her attacker, leaving Quinn and Velazquez to find her killer.

Neighborhood character Willie Bell is found naked and dead early in the morning; with nothing else to go on, Quinn and Velazquez discover that Willie was seen with two different women the night before he was found.

Quinn and Velazquez are called when Jerry Heard is found dead from gunshot wounds. They learn Heard spends his nights at a local bar, and the night he was killed, he made passes at two different women, one with an armed boyfriend. With at least three potential suspects, the detectives get to work.

21-year-old new mother, Sparkle Rai, is found by her boyfriend strangled in their apartment. He instantly becomes the only suspect, but he swears he didn't do it. Quinn and Velazquez investigate and uncover a surprising new suspect from Sparkle's past.

When U.S. Air Force veteran John Ray is found beaten and stabbed to death in his apartment, the crime scene looks like a random robbery.

Mother Shaquilla Weatherspoon is found murdered with her belongings scattered around her. To the trained eye, it looks like the killer staged the crime scene. Knowing that someone wanted it to look like a robbery, the detectives investigate those closest to Shaquilla to find the truth.

When the skull of 11-year-old Alan Watson is found in a field, Quinn and Velazquez take the case of a murder that took place almost a decade before.

After single mother Tereon Grant is stabbed to death in the middle of the night, all signs point to her ex-boyfriend being the killer. Then, Detectives Quinn and Velazquez dig deeper into the case, uncovering a dark secret that changes everything.