Swords, Blood and Bubblegum

On the day of Fionna's 17th birthday, an unpleasant surprise leads her along the path of the biggest adventure of her life. An event involving Prince Gumball needs to be fixed, and there have been many reports talking of strange crowns that change people when they are worn. Much like what happened to Betty before she become the Ice Queen.
Marshall and Fionna go on an epic quest to search for the answer behind these mind controlling crowns before their evil powers tackle another soul into the oblivion of darkness.
The two teens unlock emotions they never thought were possible when it came to one another. And there are also things stirring up in the NightO'Sphere, and Marshall is the problem, and solution, to all of them.