A mystery dinner party is a great idea for a birthday party. I just turned 12 and I had one and everybody loved it! Me and my mom bought a kit called How to Host a Teen Mystery and it came with a list of characters, a menu, invitations, and a tape that sets the scene for the crime. When everybody arrived they were dressed in their costumes. The invitations had a list of all the characters and gave costume suggestions. Since we started a little late it was a sleepover afterwards. The characters were girls and boys parts but I just had girls and nobody minded if they were a boy. what you do is you have a booklet with different clues in it and the clues are in rounds. there are clues that you have to reveal and clues that you don't have to reveal but you must always tell the truth. My package called for 8 players but since my birthday is in the summer and most people are gone, I could only get 7 people to come but it was easy because we just gave me the clues for the one person who wasn't there and it worked great. But beforehand my mom had checked to make sure that  character wasn't the criminal. She did this easily because on the last page of every book is the conclusion and what the players do is they pass their books to the person next to them and they read the conclusion in the back of the book that was handed to them. the last person's book that is read is the person who did it. It was a great and memorable party.