The document discusses different aspects of mysteries including:
1. It provides definitions and origins of mysteries, tracing them back to ancient times with one of the first published mysteries in 1841.
2. It outlines the development of mysteries over time from novels to movies, radio, television and online. Some of the most famous mystery authors and characters are mentioned.
3. Ten rules for writing mysteries are listed focusing on key elements like introducing the crime and culprit early, ensuring the crime is plausible and the culprit is capable, and not trying to mislead the reader.