Eighteen years ago, FBI Agent Rachel Ward's mirror twin, Hannah, was taken by the Gemini killer, a serial killer who delights in sending photos of his victims to their twins. Rachel assumes her sister has been dead for years, but she's never stopped hunting the monster who took her. Now, another twin has been taken, and when the case reopens, Rachel is assigned as an agent. But her relentless hunt for the killer may drive her to her breaking point.