It's time for class 1-A to start getting ready for the end-of-the-year holidays. As excited as everyone is for Christmas, New Year's Eve, and the New Year itself, preparing means undertaking a big winter cleaning. The unsuspecting students get a big surprise when their cleaning leads to a crazy discovery. There's only one way to find out where the mysterious entrance they uncover leads to--and that means rustling up some Plus Ultra spirit and venturing inside!