I haven't read a lot of mystery stories before, but my favorite story from the mystery unit was "The Speckled Band." Sherlock Holmes is the best detective, and I liked when he kept unlocking new clues and evidence to the story.
A good mystery story starter would be- One foggy morning, I was woken up at the crack of dawn by the high-pitched scream of the door bell. Still half asleep, I sauntered down and answered the door. To my surprise a young little boy appeared in front of me. " Help me please help me," he squealed. "My parents have gone missing!" I invited him in and I told him to tell me every thing that he knew about this. " Well my parents went out to dinner last night for their work, and I was left with a nanny,"he started.