When a powerful and dangerous dragon breaks free from its prison beneath the Glass Kingdom, young bookworm Glassboy sets out to find the legendary hero who first defeated the dragon centuries ago: Marceline the Vampire Queen. Marcy, now living in domestic bliss with Princess Bubblegum, is apprehensive about revisiting the Glass Kingdom. It's a place that holds bad memories for her and Bubblegum. With the help of Glassboy and some new friends, Marceline and Princess Bubblegum will have to confront their rocky past as they face off against an ancient foe.

Wizard City follows Peppermint Butler, starting over at the beginning, as just another inexperienced Wizard School student. When mysterious events at the campus cast suspicion on Pep, and his checkered past, can he master the mystic arts in time to prove his innocence?