The Lich, an evil skeleton, has escaped from his magical prison and is destroying the land of Ooo, forcing Finn and Jake to try to escape his wrath and set things right in the kingdom.

When Finn is cursed with a forgetting spell by the Magic Man, he and his friends have to try to save the Land of Ooo before he loses his memory entirely.

Squirrel Girl will encounter her most unbeatable, powerful and dangerous enemy--herself!