The best mystery I've read is "The Adventure of the Speckled Band" by Sir Arthur Conan Doyle because the speckled band actually was a snake. It's the best mystery because Sir Arthur Conan Doyle was descriptive and had unexpected twists such as when Dr. Roylott's plan back fired on him.  His plan was to kill Helen with the snake, but the snake ended up killing him!  I did not expected something like that to happen.  It is also a lot better than The Adventure of Priory School.

Here is my story starter...

Bob was doing his normal evening walk when all of the sudden something had him by his neck. He couldn't breathe! He tried calling for help, but all that come out of his mouth were high pitched screeches.  Then he died.