Cassidy Cantwell has devoted her life to becoming a detective, never forgetting the cold case that has influenced her entire career: the unsolved murder of her best friend. Cassidy tries to balance her demanding job with her suffocatingly close-knit family and her increasingly clingy boyfriend, but when a strange new murder case comes across her desk, she's determined to solve it, especially when it turns out the victim was the wife of her college ex-boyfriend.

While Cassidy's partner, Bryan, works to prove that her ex is their suspect, Cassidy can't shake the feeling that there's something more to the case that they're not seeing. After the medical examiner finds a strange ring among the victim's personal effects that the husband insists didn't belong to his wife, Cassidy is struck by similarly odd details from a previous crime scene-details that seem to have an uncanny connection to a Greek myth.

When another body attracts public attention and the FBI joins the hunt, the case gets increasingly complicated-and solving it seems further and further out of reach. With anonymous taunts about her best friend's death dragging her attention away, Cassidy finds herself pulled in different directions-sacrifice her personal life for the sake of her career or put everything she has into finding years-old answers to a case that haunts her still.

And the killer behind the murders isn't done yet.