Ice King creates a computer virus to delete everybody except him and Princess Bubblegum. Stuck inside the treehouse during a sword storm, Jake builds a pillow fort while Finn goes to a different world.
Finn and Princess Bubblegum discover a talented lemon citizen named Lemonhope while on a diplomatic trip to Castle Lemongrab; also, something strange is happening to the Earls of Lemongrab, leading to their society crumbling.
Sick and tired of babysitting Ice King while the Ice Kingdom is being rebuilt, Finn and Jake call up an old friend to hang out with their annoying houseguest: Abracadaniel. But when Ice King and his new BFF accidentally unleash the demon Kee-Oth, Finn and Jake have to clean up their mess.
Kee-Oth the Blood Demon has kidnapped Jake, taken him back to his dimension and thrown him in a pit. If Finn wants to rescue his friend, he's going to need Lady Rainicorn's help... and a videotape that will reveal how to open the portal to Kee-Oth's messed-up dimension.
Finn and Jake accompany Princess Bubblegum on her study of the Desert of Wonders. However, they are soon attacked by goo monsters, and Finn and Jake think that Bubblegum's robot helper James is to blame.