By now you have read and listened to different mystery/detective stories. You have presented your story to an audience. It is your turn now to write your own mystery story. You will have to include all the necessary elements that make a story a mystery one: victims, witnesses, suspects, red herrings, crime, crime scene, clues, suspense, intrigue...
Rememeber that you have to plan your story carefully.
Let's be writers for a day!