On the night of their twenty-first birthday, Brooke Leighton's twin brother is mysteriously murdered in a back alley. The mystery surrounding Bobby's death is never solved, which leads to her unquenchable thirst for justice and a rising career on the police force. Seven years later, her birthday is still a constant source of discord for her, and no matter how hard she tries to celebrate, she often struggles to just get through the day. This year is no exception when a ghost from her past crashes her party, sending her carefully constructed life into a tailspin and unearthing everything she's worked so hard to bury. Her life is only further complicated when she is assigned to a homicide investigation that mirrors her brother's murder. While examining the crime scene with her partner - and current love - Brooke hears a strange noise. Thinking it might be the suspect, she investigates, but what she initially thinks is a large dog turns out to be anything but. Unfortunately, Brooke does not escape this encounter unscathed, and she is left with more than just the physical scars to remind her of the night her life was unknowingly and irreparably altered. When the next full moon rises, an entirely new world is opened up to Brooke, unlocking the secrets behind the investigation and her brother's unsolved murder.