A mysterious disappearance. A glowing symbol painted on a crumbling wall. Sentient smoke that chases, chokes, and burns. Bridget Keene practically raised her little sister. Then Dahlia vanishes. Her car is found submerged in the river, and nine months later, everyone has given up hope. Everyone except Bridget. She's determined to revive the case and bring Dahlia home. Except her search reveals something far more sinister than a typical missing persons case - a carefully-guarded plot tied to powerful, ancient magic. To uncover the truth about her sister's disappearance, Bridget will confront a secret world that threatens to drag her under, too.