Finding their friend, Marceline the Vampire Queen, in a deep sleep, a mysterious stranger helps Finn and Jake by sending them into her dreams to awaken her.
Finn is happy that Princess Bubblegum has regressed to the same age as him. But soon a challenger for the throne arrives to unseat the newly underage princess.
In order to open a magic door filled with stolen items, Finn and all his friends must perform in a band. But everyone's differing musical tastes and overall tensions make things difficult.
After trying to stop a deer that has been licking the Candy Kingdom people, Finn wakes up in a hospital to find everyone missing except Jake who is acting very strange.
Bored waiting for her, Finn and Jake sneak into Marceline's house, become trapped when she comes home, and witness her strange behavior when she's alone.