In the end, the mystery has to make sense. As part of this, the characters have to be consistent, the timeline should be linear, and all relevant information must have been presented. When the detective explains at the end how he figured it out, the reader should feel a little surprised that they weren't able to figure it out too. After all, the solution should make sense.
- Red Herrings
Of course, one of the reasons the reader didn't figure it out is by the liberal use of red herrings. This is where the author gives great literary weight to inconsequential things but pays only a passing glance to relevant, important information. Agatha Christie is great at hiding the obvious amongst a plethora of random facts. In almost all of her mysteries the most obvious solution is the correct one -- the husband kills the wife, the wife kills the husband, etc. In fact, these people are almost always suspected in some way or other before initially being exonerated. She confuses the issue with so many false (but plausible) trails that everyone gets taken in. In fact, if someone is serious about writing a mystery, even one without murder, I would recommend reading Christie's The Mysterious Affair at Styles and The Murder of Roger Ackroyd. Quite a bit can be learned about mystery plotting by studying these books.
- Protagonist Solves the Mystery Him/Herself
This is the problem I come across the most when reading mystery manuscripts. The piece will be proceeding in a normal mystery fashion and then instead of the kid solving the mystery, a helpful (normally adult) person steps in and explains it all. This is the big difference between Harry Potter 1 & 2 and Harry Potter 3-7. In the first 2, Harry and friends figure everything out on there own each time. They discover what's being hidden in Hogwarts or the location of the Chamber of Secrets and the type of beast within all by themselves. In the rest of the books, Dumbledore tells Harry everything. This doesn't make them bad books but it just makes them mysterious instead of actual mysteries.
Posted by The Buried Editor on 11/06/2009
So far I've mentioned what I don't like to see in a mystery story, but what exactly goes into making a good mystery? Here are my ideas for a fun, exciting mystery: