When Mary and her friends try to take stock of all the academy's derelict unapproved research projects, they stumble upon an underground room housing a small box. Surely, whoever went to the trouble of putting this box so far out of the way must've thought no one should ever open it under any circumstances...a fact that becomes all too apparent after the prince dons the magic tiara inside and finds it impossible to remove! Far from merely being a very persistent accessory, the prince's new headgear is an ensemble piece, lengthening his hair and granting him a feminine physique—as best as anyone besides Mary and co. can tell, he's now a beautiful young girl. Fearing for her behind if word should get out about what befell the prince under her watch, Mary gets on the case to find a way to peel the tiara off his noggin. Will the invincible little lady manage to lift the prince's curse before it's too late? And all the while, the world's oldest, strongest vampire begins to make her move...