|The following information is from the Adventure Time comic book series.|
It may not be part of the same canon or continuity as the animated series.
Issue 21 of the Adventure Time comics.
"Finn and Jake find themselves in a sticky situation when Princess Bubblegum's experiments searching for the origin of life...specifically, her life...go horribly wrong, overcoming the Candy Kingdom! What sour weapon can the boys find that can overcome something so primordially sweet?"
In the Candy Kingdom, Princess Bubblegum is getting ready for the day until she realizes how unappealing the tasks are and has Peppermint Butler cancel them. Princess Bubblegum then talks to Peppermint Butler about her worries about the safety of the Candy Kingdom, between the constant attacks and the story Finn and Jake told her about trip to the future, Princess Bubblegum realizes that they only need to mess up once to lose forever. The conversation is cut short when Marceline shows up early for lunch. Princess Bubblegum asks Marceline how to best protect her kingdom and express an interest on trying to find protection for the kingdom instead of constantly relying on Finn and Jake.
In the Candy Kingdom, the Gum is erupting through the floors of Princess Bubblegum's room. Peppermint Butler attempts to fend it off, but gets engulfed by it.
At the Tree Fort, Finn, Jake and BMO are forced to leave the Tree Fort as the Gum overtakes it, complaining that their home is constantly damaged by evil-doers. They run away as the Gum follows them.
Back at the Candy Kingdom, Princess Bubblegum has the Banana Guards lock the castle doors and uses a experimental fire extinguisher to cover the room in five layers of jawbreaker candy and calls Finn and Jake to gloat that she's taken care of the problem.
Finn and Jake have outrun the Gum and are close to the Candy Kingdom when BMO alerts them to a call from the Princess who quickly brags about her victory over the Gum before hanging up. Finn and Jake are offended of how fast the call was and how quickly she hung up before they had the chance to congratulate her until BMO points out it's a recording. It turns out Princess Bubblegum made the call thirty-six hours ago, but Finn and Jake were still in bed at the time and just told BMO to set alarm to remind them later.
Finn and Jake go to look at the Candy Kingdom and it's covered by the Gum.
Back up story
Beach Bum Boogie
Finn and Jake find two magic surfboards and fight a sea monster.
Comic preview pages and panels