Now 17, Finn the Human has become a mature hero of Ooo. However, repressed feelings for Flame Princess are desperately trying to tear him apart, and the fiery girl knows his pain. As an ancient evil rises to consume all existence, a final chance will present itself to Finn and his friends to not only stop the madness but finally unite a couple struggling for each other's love.

Set after Earth and Water. Ever since the new Flame Queen enacted the law of total honesty, she has been very busy with her citizens. Even with Finn's help, she remains occupied with her duties. With time almost running out for them, will they still find a way to restore their relationship?