When Lexie's fiancé runs off with her so-called best friend on her birthday, her carefully crafted fairy-tale life shatters. To distract herself, Lexie throws herself into her unusual job: matchmaking psychopaths (a specialty her clients are blissfully unaware of). But the loneliness is crushing. So when a gorgeous, overprotective new client named Aidan insists they're soulmates, and another intriguing client, Rebecca, seems perfect to fill the best-friend-shaped hole in her life, Lexie can't help but find the attention comforting --- despite her own professional boundaries. Then a human heart appears on Lexie's doorstep. As more threatening packages arrive and her fiancé mysteriously disappears, she must confront a terrifying question: Did she inadvertently match herself with a killer?

Recently ghosted and sick of watching her friends fade into the suburbs, thirty-something Hannah finds community in a true-crime forum that’s on a mission to solve the murders of four women in Atlanta. After William, a handsome lawyer, is arrested for the killings, Hannah begins writing him letters --- and he writes back. Her interest in the case goes from curiosity to obsession, leaving space for nothing else as her life implodes around her. After she loses her job, she heads to Georgia to attend the trial and befriends fellow true-crime junkies. When a fifth woman is discovered murdered, the jury has no choice but to find William not guilty, and Hannah is the first person he calls upon his release. The two of them quickly fall into a routine of domestic bliss. Well, as blissful as one can feel while secretly investigating their partner for serial murder.