For my daughter's 13 birthday we had a mystery dinner party. We made invitations by using cut-out letters from magazines. You are invited to a mystery dinner, date, time and place. Another idea would be to send an invitation with the words backwards that can only  be read by using a mirror. When the girls arrived the butler (my husband) welcomed them to the mystery dinner house. After all of the girls arrived they were escorted to the dining room. Decorations included question marks cut out of construction paper and placed on the walls and table. Each girl received a menu. The girls would need to fill out their own menu. We had a four course meal. Each course included four items that the girls had to choose from a selected list of menu items. The mystery was the menu items are described in the way that the girls did not know what they were ordering. For example, rabbit food was really carrots. Come up with your own creative menu. After we collected all of the menus the girls were served what they ordered. Some received all of their utensils for their first course, and had to eat the rest of the food using their fingers or by finding  another creative way. The girls had a  great time! Thank you notes were made out of pictures of the girls at the party.