These six questions are the absolute core of mystery play. When you create your adventure you need to answer these questions, and these are the answers the characters are seeking.
If you know the answers to these six questions, you know your mystery will hang together, and if you need to create clues on the fly, probably because you players have different ideas to what you have planned for, you have all the tools you need.
If you know the truth, it is easy to imagine what evidence may have been left behind, or who may have been a witness.
If the mystery is still playing out as the characters are in the midst of their investigation, you know what the villain of the piece is going to do next, and why. If the characters disrupt those plans you still know what the villain needs to achieve.
This is your foundation from which you can build any mystery.
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