Good mysteries have twists and turns that seem inevitable in hindsight but spring surprises on first-time readers. So how do you pull that off and maintain a solid, logical structure? The answer lies in planning before you start writing. Plotting the major events in advance will avoid plot holes and keep your story moving quickly. Here are some ways planning the plot can get your novel off to a running start:
You begin by brainstorming major plot points – the inciting incident, main turning points, and climax. Jot these down roughly in chronological order. This “plot skeleton” ensures all the pieces are in place before you dive into writing the first draft.
Next, think through how to connect these major events in a logical way. Fill in the scenes needed to move the story and characters along in a believable fashion. As you do this, look for opportunities to lay foundations for plot twists and red herrings. Foreshadowing and subtle clues will make plot developments more satisfying for readers.
As you refine your story outline, continue editing and rearranging plot points to improve the flow and pace of your story. A well-planned mystery novel will impress readers with its inevitability while still catching them off guard. So before you start writing, take the time to plan the perfect crime – on paper.
Chris The Story Reading Ape's Blog 
A great article, it is easy to see the benefits of “planning” and Zara clearly has her plan in mind. Alas, I do little planning, little development and pay scant attention to characters. Yet I manage to put the shock Zara mentions into most of my books (some do not require it).
Once the editor of science fiction, horror, and mystery tales’ magazines, the unexpected twist was our stock in trade. Most of the stories were written by other authors, of course, but it gives you a taste for the dramatic. The twist in the tale or unusual ending.
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