On Caspian's Unbirthday, his grandpa always gives him a silly present that just isn't right for a birthday present. This year it's brown underpants. Caspian is disappointed. Grandpa calls them "Hot Chocolate Underpants." Then he spills cocoa on Caspian's lap. Caspian glares at his grandpa. Grandpa smiles. Then Caspian's butt twitches. The adventure begins.