Penny and her detective friends are thrilled: their favorite teacher, Mrs. Weinerlein, is finally marrying the school janitor, Mr. Ortel. So they need a great gift. A toothbrush holder? Slippers? A diving suit? Penny, Ida, Marie, and Flora rack their brains and finally come up with a brilliant idea: to make and decorate the wedding cake, with the help of a French pastry chef. The perfect gift and the ultimate surprise! Everything seems ready for the big day. But then the cake disappears...