When Twilight starts blacking out and sees a figure cloaked in darkness she starts wondering who or what he is when she seeks help from Cadence she looses control and almost hurts her, with dark magic no less. Twilight doesn't dare go to Princess Celestia for help, Celestia wouldn't understand so she turns to the pony in her head. When she does, she sign's her soul to the King of Shadows, King Sombra. Her old enemy becomes her teacher and makes her do things to others she never even dreamed about. Twilight has gone off the deep end can her friends save her before it's to late?