After the demise of King Sombra, the royal sisters seized his personal writings for study and eventually to seal them away. However, half of his journal is stolen by Golden Jubilee, a sorceress from the secretive organization called the Horizon Walkers. Team Trixie is hired to recover this journal before the Walkers can learn of the dark knowledge the late king had written within them.

As the investigation brings Trixie close to the Walkers, she uncovers how Golden knew of the hidden half of the journal and just what reason the Walkers want the second half. Trixie must confront a past fear as the trail leads her to an old artifact she is uncomfortably familiar with - The Alicorn Amulet.