After dozens of Lexington, Kentucky's forgotten—mostly prostitutes and the homeless—swamp local hospitals from apparent overdoses over the 4th of July weekend, Kentucky cops soon discover a new synthetic form of heroin is infecting their communities, and that gangs—namely the outlaw motorcycle gang Samael's Army—are responsible for using a "disposable" population to test the new drug.

Soon after, the deadly new drug claims the daughter of a U.S. senator, and FBI Director Jack Waller assigns Brooke Fairfax to the case. Because the synthetic opioid was created in a lab, the feds turn to the expertise of billionaire chemist Declan O'Roark, who is all too happy to lend a hand if it will bring him closer to Brooke.

As Brooke and Declan are forced to work together, Declan attempts to tear down the barriers around Brooke's heart. But when Brooke gets drawn into the depths of the outlaw motorcycle gang she's investigating, she and Declan both fear for her life.