Mercy Black tells the story of Marina Hess, who stabbed a classmate fifteen years ago in an attempt to conjure an imaginary phantom named Mercy Black. Now, after being released from psychiatric care, Marina is returning home to live with her sister and young nephew.
Since Marina's crime, the myth of Mercy Black has spread like wildfire on the internet, inspiring rumors, stories, and even copycat crimes. Marina is tormented by her past actions and the phantom she created, but her nephew becomes fixated on Mercy Black.
To protect her nephew, Marina must confront her past and uncover the truth behind Mercy Black. What she uncovers is a chilling reality - a deadly horror that will stop at nothing to claim her and her nephew.