The sleuth knowing something that he couldn’t possibly know or the plot completely running out of steam before you are halfway through. It’s important that the writer knows the explanations behind everything that happens in the novel, even if she hasn’t shared it with the reader – yet.
Obviously, most mystery writers know who the killer is from the word go, but they don’t normally tell the reader in the first chapter. But revealing – in that Hercule Poirot-style final scene -that the killer is a character the reader has never heard of before just won’t work. As a writer you aren’t only a creative artist; you are also the master architect of your novel and it is your job to make sure that everything in the story makes sense – otherwise the book will come crashing down round everyone’s ears.
While it may seem impossible to alter an idea that’s already in place, asking ‘What if …?’ helps in that situation as well. Don’t be afraid to make sweeping changes if you find yourself wrestling with something that just isn’t working. What if you altered the setting? What if Paris became New York and the 1890s became the 1920s? Look at it from a different angle and you may come up with something fresh and sparkling.