[header] How to write a mystery story [title] Understand the distinction between the mystery genre and the thriller genre. [step] Mysteries almost always begin with a murder. The major question in a mystery is who committed the crime. 
Thrillers usually begin with a situation that leads to a major catastrophe, like an assassination, a bank robbery, a nuclear explosion, etc. The major question in a thriller is whether or not the hero can prevent the catastrophe from occurring.