After a disastrous morning, a down-on-her luck Fionna seeks treatment for an out-of-sorts Cake.

While Cake crash-lands in a fantastic new world, Fionna continues her search after witnessing something impossible.

Pursued by a powerful enemy, Fionna, Cake and Simon venture through a lawless world in search of a magical artifact.

Cake is recruited by a band of skilled vampire hunters. Gary and Marshall Lee attend a black-tie party.

While Simon experiences a cosmic detour, doom closes in on Fionna and Cake.