It's the winter holiday break in schools. Even in roxfort. Kassy and Xiao have to spend the holiday at the dorm for some family resons. They get bored quickly.
Kassy decides to try some spells on Xiao and the other way around. Their experimentation gets more and more out of hand until one day Kassy decides to freeze Xiao with "petrificus totalus". The full body bind curse works marvelously on the unsuspecting Xiao. Rendering her motionless. Kassy can finally try some other kind of experimentations on her girlfriend and long time roommate.