Finn summons the Lord of Evil, Hunson Abadeer, in an attempt to get him to reconcile with his daughter, Marceline. But, after being summoned, Hunson chooses to go on a soul-sucking rampage instead.
Nervous about giving a speech at Princess Bubblegum's science conference and barbecue, Finn finds a magical pair of glasses that make him the smartest being in the land.
The Lich, the greatest form of pure evil in the land of Ooo, is accidentally unleashed. With the highest stakes, Finn and Jake set out on the most serious adventure of their career.
Finn and Jake ask Marceline the Vampire Queen to turn them into vampires. However, she isn't interested in transforming her friends and tricks them into thinking she has.