Amid a sultry Atlanta summer, someone is targeting police. The investigation becomes personal for APD Detective Ryan Winter when a colleague and friend is shot dead—the second victim in weeks. But even as he finds himself being drawn into the tense hunt for a serial cop killer, he is forced to reexamine his own shattering personal tragedy.

An ER physician at Atlanta's busy Mercy Hospital, Dr. Lydia Costa is no stranger to suffering. Still, the recent police slayings reopen barely healed wounds—and bring her face-to-face with her ex-husband, Ryan Winter. As the body count rises and paranoia tightens its grip on the police force, Lydia and Ryan are pulled together by circumstances and fate, causing old passions to reignite despite their painful shared past. But as Ryan moves closer to discovering the killer's identity, someone is watching, placing both him and Lydia in mortal danger.