Advent-urous Calendar

James and Peter have a plan to get a secret out in the open while adding some festive and holiday cheer around Hogwarts. Remus loves Advent Calendars; Sirius has no clue what they are but is curious as a cat. They make a very special Advent Calendar that they know neither can refuse using. But what is the challenge that lies behind door 25 on the calendar? Rated T for later chaps