Mysterys are circular by nature. Their construction is circles within circles. Because of the shape of a mystery there are many different points of entry when devising a cluetrail. In the centre of the circle is the crime. Around the circumference are the suspects. Orbiting between the centre and the circumference are the motive, method, opportunity - any one of them a point of entry into creating and solving a mystery. You can start with the big picture of what actually happened or begin with a small portion of the picture; motive, method or opportunity.