In a special episode, Fionna (the gender-swapped version of Finn) puts up with the sudden courtship of Prince Gumball while taking advice from her partner Cake in dealing with guys.
The episode opens with an alternate version of Finn and Jake's, with gender swapped characters. Fionna and Cake are helping Prince Gumball decorate for the Biennial Gumball Ball, when Prince Gumball asks Fionna if she would like to go with him "as pals ". Their conversation is interrupted when Cake’s tail frizzes at the coming danger. Fionna rushes to the balcony and sees the Ice Queen coming down from dark clouds to kidnap Prince Gumball. She breaks into the castle, forms a slush beast around herself and goes after Gumball. Cake turns into a morning star that Fionna uses to smash the slush monster, with Ice Queen and Gumball inside.
The room fills with snow, and Prince Gumball appears unharmed but Ice Queen has mysteriously vanished. Prince Gumball then asks Fionna to "go out" with him, and Cake agrees for her to meet him again in an hour at the Castle Gardens.
At the Tree Fort, Fionna and Cake argue over whether or not Gumball asked Fionna on a date. Cake insists that it is and decides to come along to help Fionna, taking her dulcimer with her as a “conversation starter” (the alternate to Jake’s viola, apparently.) Fionna begrudgingly agrees to this, and they go meet Prince Gumball at the Castle Gardens. Prince Gumball is joined by Lord Monochromicorn. Prince Gumball gives Cake a satchel of catnip that Lord Monochromicorn picked himself, and gives Fionna a bouquet of posies with a retractable crystal sword inside it. Fionna is more excited by the sword than the flowers.
The group rides off, and Prince Gumball challenges Fionna to a race to Marshmallowy Mweadows . The group races there, and Fionna and Prince Gumball jump off their friends into the flowers. Suddenly Prince Gumball dives into the squishy ground and disappears. Panicking, Fionna dives after him and pulls him out. Gumball explains he saw a pearl pygmy skull in the flowers that reminded him of Fionna's sparkling eyes. Later the group flies off on Lord Monochromicorn, and Prince Gumball sings about Fionna, and Cake plays along with her dulcimer. The flight ends when Cake and Lord Monochromicorn drop Fionna and Prince Gumball off in a grassy field, leaving them alone together. After lying on the ground talking for a while, Prince Gumball asks Fionna to come to the ball with him as his girlfriend.
Fionna rushes back to the Tree Fort and tells Cake that she is now going to the ball as Gumball’s girlfriend. After Cake dresses her up in a fancy gown, Fionna asks how she’s supposed to fit weapons in her purse. Cake says she doesn’t need weapons at a ball, but Fionna takes the retractable crystal sword with her anyway.
When Fionna and Cake get to the ball, Prince Gumball takes Fionna to his room, decorated with candles and rose petals, and locks the door. She becomes flustered when he begins to take his shirt off. A drop of water lands on her shoulder, she looks up to see the real Prince Gumball trapped in a giant icicle on the ceiling. The fake prince is revealed to be Ice Queen in disguise.
Enraged by the deception, Fionna takes out the crystal sword to fight, but the sword is another one of Ice Queen’s tricks and turns into a ball of ice around Fionna’s hands. Cake hears noises from downstairs and senses Fionna is in trouble.
Undaunted, Fionna uses the ice to beat Ice Queen over the head. Ice Queen pushes her off in burst of snow, which Fionna uses to get close to enough to break Prince Gumball free. Ice Queen gets knocked down by the broken icicle pieces just before Cake bursts into the room. Seeing Gumball standing next to Fionna in her torn dress, Cake jumps to the wrong conclusion and lunges at the prince. Fionna stops Cake from hurting Gumball and tells her it was the Ice Queen all along.
Just then Ice Queen recovers and blasts Cake away from Fionna with an ice blast. Fionna knocks her magic tiara off, squelching her powers, and then punches her for "yanking her heart-guts". Cake then uses the tiara’s power to bury the Ice Queen in snow. The real Prince Gumball is impressed by Fionna and asks her on a date, but she turns him down. Fionna decides she doesn't need a boyfriend, but adds that she would love to date the Ice King. Then the scene changes to the real Ice King’s throne room, where he is reading a fan fiction he wrote to Finn and Jake, who are trapped in ice.