If you want to write a ‘fairplay’ mystery – where your reader has all the clues to solve the mystery- the earlier you plant the clue that will give away the solution the better. Below is a case in point. Good old Sherlock!
Sherlock Holmes and Dr. Watson went on a camping trip. After a good meal and a bottle of wine, they were exhausted and went to sleep.
Some hours later, Holmes awoke and nudged his faithful friend.
“Watson, look up at the sky and tell me what you see.”
Watson replied, “I see millions and millions of stars.”
“What does that tell you?” Holmes said Watson pondered for a minute.
“Astronomically, it tells me that there are millions of galaxies and potentially billions of planets. Astrologically, I observe that Saturn is in Leo. Timewise, I deduce that the time is approximately a quarter past three. Theologically, I can see that The lord is all powerful and that we are small and insignificant. Meteorologically, I suspect that we will have, a beautiful day tomorrow. What does it tell you?”
Holmes was silent for a minute, then spoke. “Watson, you idiot, Some ——- has stolen our tent.”
The very first piece of information you were given is that they were camping. But after the good meal, the bottle of wine and the lengthy discussion about the meaning of the universe, you forgot that. Ta Da.