Finn and Jake was seeing Marceline today for hanging out with her but she was sad about something. Then Hunson Abadeer told the boys that Marceline was invited to the underwold prom but she have no one to go with. Then Finn got an idea that he disguise as a good looking guy that want to ask Marceline out to the prom. So the guys meet up at their home with Hunson Abadeer. Jake makes Finn's blond hair into emo dark and his clothes too. Abadeer finished it up with a aging spell that turn Finn 18 years old and shows him how to act dark like Marceline. So when everthing was ready it was time introduce the new Finn without telling to Marceline that was Finn or she would go beserk of going out with 13 years old boy. So Finn was acting all dark cool and says wanna go to the underworld prom and Marceline was so in love him before they go she ask what his name but Finn was not good with dark cool names so he name himself Ferr even thought it meant to say fear it sound kindly girly that what Hunson say while hiding to see if the plan work. Marceline notice something odd about the name but was distracted by the Finn's disguise who looks her soulmate.
When they go, she was carry him to the underworld while going all they do was talking before entering the prom building and Marceline and Finn had so much fun until something happens, Ash was also there with his new vampire girlfriend named ????????. Marceline was like all mad and Ash was laughing on Marceline that she couldnt find anyone, but Marceline say she did and he is right besides me and he is totally not a jerk like you. Then Ash was seeing Ferr and say he doesn't look that tough and those are pretty lame together. Finn couldn't take it anymore of Ash insulting them so he pull out his sword and says I want to say it again at my face. Ash wasnt scared so he called his home boys Scorcher and Magic Man and ask them to take him on. Maceline says we should back off because she doesnt want to see Ferr get hurt. Even thought Finn know his enemies how they fight he was still wasnt scared. So he charge at them with his blade.
It was an epic fight between Finn vs Ash, Magic Man, and Scorcher. At the end he won, no one got killed and he got ash to say sorry to Marceline. After that Marceline and Finn was slow dancing together and then the announcer tell everyone the prom king and queen and it was them. Finn was glad everthing was fine and Marceline was so happy that she was trying to kiss Ferr mouth to mouth but then the aging spell worn out and when she open her eyes after kissing him it was not Ferr this whole time but Finn. Jake, who was spying on them, was thinking Marceline will goes berserk on him so he grab Finn and ran off. Ash and his home boys was laugh out by everyone in the prom for being beaten by a kid. Marceline who would expected to go beserk but instead she blushed and said Finn is so amazing. No one saw that because eveyone was laughing at Ash and his gang except for Hunson was also spying on her and Finn and his expression was a smile for Marceline express her emotions about Finn.