Seventeen-year-old Amanda is a Ghoster, capable of traveling between Shadows of Onyx to talk to ghosts and summon demons, but wishing only to devote her life to music.

Everything changes when Eric, her best friend and bandmate, sends her a cryptic request to meet at the annual alumni masquerade, along with a legendary Mask of Onyx to wear at the ball. But before they have a chance to talk, Eric is kidnapped by the headmaster and Amanda is forced to infiltrate the dangerous Sphere of Onyx in a land she knows only from stories whispered in the school corridors.

Spiraled into a world of betrayal, ancient battle and love, Amanda must reach the deepest source of her magic to find Eric before he is sacrificed, risking losing her soul, her best friend and the way back home forever.