The best mytery story that I have read was The "Speckled Band" by Sir Arthur Conan Doyle. I think it is the best because I don't read that many mystery books except when we did the 8 short stories. The "Speckled Band" stood out to me because first it was one of the must reads and second I liked how sherlock manipulated the snake.
If I were to write an intro to a mystery story the story would begin with a guy being murded in the pool table area of the Ripley Star Club. I would then have it be found by the bar tender when he was closing up the shop. He would call the police wich would follow clues and try to find the murderer. In the end I would have them die Grisly deaths.