I didn’t start my novel by writing an outline. I went at it haphazardly. I had my beginning, and I knew what my ending would be, but I only had vague ideas about exactly what would happen in the middle. And in a mystery, what happens in the middle is pretty important.
I’ve heard one writer of excellent mysteries say that everything that happens in the mystery novel needs to advance the story in some way. That makes sense. But it’s not possible to make that happen in a haphazard manner. That same writer said that if, as an author, you’re not a person who uses outlines, that you’ll become one.
And I did. I realized that I needed to have a step by step layout of what needed to happen to get my mystery story from point A to point Z. So I made my first outline.
The finished story doesn’t look like that first outline. I made a second outline a little later, which was much more detailed and contained all those plot points that needed to exist to get the story told and the mystery solved. Then it became easy to see where things didn’t make sense sequentially, or where something else needed to happen between two points.
It also helped me see what scenes still needed to be written. So, while I was finishing the book, I could refer to the outline and see what scene I wanted to write that day. And that would be the scene that I’d write on 750words.com that day.
So, yes, outlines are necessary for mystery writing. It would be tough to do without them.